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Adjuvant Chemotherapy for Stage III Colon Cancer: Do Physicians Agree About the Importance of Patient Age and Comorbidity?

Nancy L. Keating, Mary Beth Landrum, Carrie N. Klabunde, Robert H. Fletcher, Selwyn O. Rogers, William R. Doucette, Diana Tisnado, Steven Clauser, Katherine L. Kahn

From the Division of General Internal Medicine and the Department of Surgery and Center for Surgery and Public Health, Brigham and Women's Hospital; the Departments of Health Care Policy and Ambulatory Care and Prevention, Harvard Medical School, Boston, MA; Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD; the Division of Clinical and Administrative Pharmacy, University of Iowa, Iowa City, IA; RAND, Santa Monica; and the Division of General Internal Medicine, University of California, Los Angeles, Los Angeles, CA

Corresponding author: Nancy L. Keating, MD, MPH, Department of Health Care Policy, Harvard Medical School, 180 Longwood Ave, Boston, MA 02115; e-mail: keating{at}hcp.med.harvard.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION AUTHORS' DISCLOSURES OF... AUTHOR CONTRIBUTIONS APPENDIX REFERENCES

 
Purpose We surveyed cancer physicians to understand how patients' age and comorbidity influence adjuvant chemotherapy recommendations and whether physician or practice characteristics also affect these recommendations.

Methods National survey of surgeons and medical oncologists caring for patients with colorectal cancer regarding whether they would recommend adjuvant chemotherapy for hypothetical patients with stage III colon cancer who varied by age (55 v 80 years) and comorbid illness (none, moderate, severe congestive heart failure [CHF]). Repeated measures logistic regression was used to assess the influence of patient, physician, and practice characteristics on chemotherapy recommendations.

Results Of 1,096 physicians, nearly all recommended chemotherapy for patients who were 55 years old with no comorbidity (99.0%), 55-years old with moderate CHF (88.6%), or 80 years old with no comorbidity (92.6%); many fewer recommended chemotherapy for 55-year-old patients with severe CHF (24.9%) or 80-year-old patients with moderate (47.2%) or severe (9.0%) CHF (P < .001). Younger physicians (P < .001) were more likely than others to recommend adjuvant chemotherapy overall, although physician factors explained little of the variability in recommendations.

Conclusion Physicians agree with guidelines recommending adjuvant chemotherapy for young, healthy patients with stage III colon cancer but differ widely on recommendations for patients who are older and sicker. Few physician or practice characteristics were associated with recommendations. For older and sicker patients, the individual physicians seen may have a substantial impact on the likelihood of receiving chemotherapy. Understanding better the sources of variation not explained by patients' clinical characteristics may allow improved tailoring of therapy to patients most likely to benefit.

	INTRODUCTION

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Adjuvant chemotherapy with fluorouracil-based regimens improves survival for patients with stage III colon cancer.^1-6 Although few studies have directly compared effectiveness in younger versus older patients, a pooled analysis of seven randomized trials of adjuvant chemotherapy for resected colon cancer demonstrated that selected elderly patients with colon cancer receive the same benefit from fluorouracil-based adjuvant therapy as their younger counterparts without a significant increase in toxicity.⁷ In this analysis, the 5-year overall survival for patients who received adjuvant chemotherapy was 71% versus 64% for those untreated. Similar benefits have been reported in population-based observational studies of older patients.^8-10 Nevertheless, many patients who might benefit from adjuvant chemotherapy, particularly older patients, do not receive this treatment.^10-15 Whether this reflects appropriate decisions by physicians and patients or age-related disparities is not well understood. Moreover, it is unclear whether physician or practice characteristics contribute to lower use of chemotherapy.

Because 80% of recurrences occur within 3 years and 90% of patients with recurrence die within 24 months,¹⁶ patients with a life expectancy of more than 5 years are most likely to benefit from treatment. The life expectancy for an otherwise healthy 70-year-old patient is nearly 15 years, and almost 9 years for an 80-year-old patient.¹⁷ Yet life expectancy decreases with comorbid illnesses. For example, a 71-year-old patient with stage III colorectal cancer and three or more additional chronic illnesses has a life expectancy of approximately 4 years.¹⁸ As life expectancy decreases, the absolute benefit of chemotherapy also decreases. Thus, for patients who are older and have comorbid illness, the absolute benefit of adjuvant chemotherapy may be small and decisions to forgo treatment may be appropriate given the patient's overall health status.

To understand better the influence of patient age and comorbidity on physicians' recommendations for adjuvant chemotherapy, we surveyed surgeons and medical oncologists who care for patients with colon cancer. The objectives of our analyses were to examine whether: physicians' recommendations for chemotherapy vary by patients' age and comorbidity; physicians agree about the relative importance of patient age and comorbidity when recommending chemotherapy; and physician or practice characteristics influence physicians' reports of recommendations for adjuvant chemotherapy.

	METHODS

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Study Design
Data were collected as part of a national study of variations in care and outcomes of care for patients with lung or colorectal cancer undertaken by the Cancer Care Outcomes Research and Surveillance (CanCORS) Consortium.^19,20 CanCORS is examining care delivered to population-based cohorts totaling more than 10,000 patients diagnosed with lung or colorectal cancer during 2003 to 2005 living in Northern California, Los Angeles County, North Carolina, Iowa, or Alabama, or who received care in one of five large health maintenance organizations or 10 Veterans' Administration Health Care System sites. Data collection included patient interviews, medical record abstractions, physician surveys, and surveys of informal caregivers. The study was approved by the human subjects committees at all participating institutions. This analysis uses only physician survey data.

Study Population
We surveyed physicians named by patients as providing important roles in their care. Of the 6,871 physicians whose contact information was verified, 4,188 (61.0%) responded. Respondents did not differ by sex (P = .97). Radiation physicians versus other physicians and those graduating from medical school before 1976 or after 1989 versus 1976 to 1989 responded more frequently (both P .005). We restricted the sample to the 1,123 physicians who identified themselves as surgeons or medical oncologists and who cared for at least one patient with colorectal cancer in the past year. Further details on the survey is provided in the Appendix (online only). We used data version 1.6.1, locked March 2007.

Survey Instrument
To understand the influence of patient age (55 v 80 years) and level of comorbid illness (none, moderate, severe) on physicians' recommendations for adjuvant chemotherapy, each physician responded to the following scenario: how likely are you to recommend adjuvant chemotherapy (ie, chemotherapy that is provided in addition to surgery) for the following patients who underwent curative resection for stage III colon cancer: a 55-year old man with stage III colon cancer who has (1) no other medical problems; (2) moderate congestive heart failure with dyspnea walking 2 blocks (ejection fraction 35% to 40%); (3) severe congestive heart failure with dyspnea on dressing (ejection fraction < 20%)? Physicians responded using a 4-point Likert scale where 1 = very unlikely, 2 = somewhat unlikely, 3 = somewhat likely, and 4 = very likely. The scenario was repeated using an 80-year-old man as the patient. Physicians also provided information about personal and practice characteristics.

Statistical Analysis
Item nonresponse was less than 2% to 3% for most variables. We excluded 33 physicians who did not respond to four or more of the items on chemotherapy recommendations. The final sample included 1,096 physicians. We used multiple imputation to impute missing data for remaining items.^21,22

We categorized physicians' recommendations for chemotherapy as very/somewhat likely to recommend versus very/somewhat unlikely to recommend. We dichotomized because the response options were not linear; however; sensitivity analyses considering the Likert scale as linear or ordinal produced similar findings (data not shown).

We summed these dichotomous variables to create a single variable reflecting the number of scenarios for which each physician recommended treatment. We compared the number of recommendations for chemotherapy by physician and practice characteristics using bivariate analysis of variance (the distribution ranged from 0 to 6 with a mean of 3.61; standard deviation [SD], 1.18; median, 4, and approximated normal). Specifically, we assessed associations with self-reported physician specialty, age, sex, race/ethnicity, board certification, United States medical graduate, teaching involvement, practice site, percentage of patients in managed care, geographic site, number of colorectal cancer patients cared for in the last month, base clinical income, whether income changes as a result of prescribing/administering more chemotherapy (medical oncologists only), whether their practice is part of the Community Clinical Oncology Program (CCOP), whether they practice at a National Cancer Institute (NCI)-designated cancer center, attendance at tumor board meetings, and whether they enroll patients onto clinical trials. Variables were categorized as in Table 1.

In secondary analyses, we tested for interactions between patient characteristics and physician characteristics that were significantly associated with chemotherapy recommendations. Next, we repeated analyses stratifying by specialty (surgeons v medical oncologists). All tests of statistical significance were two sided.

	RESULTS

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The mean age of the physician cohort was 49.9 (SD, 9.6); nearly half were general surgeons, 9% were colorectal surgeons or surgical oncologists, and 43% were medical oncologists (Table 1). Most physicians (84%) were male and more than half (51%) were engaged in teaching. The mean number of years since medical school graduation was 23.3 (SD, 9.9). Physicians saw an average of 10.2 (SD, 13.8) patients with colorectal cancer in the previous month (median = 5).

Physicians' recommendations for adjuvant chemotherapy varied substantially by patient age and severity of comorbid illness (Fig 1). Nearly all physicians (98%) were very likely to recommend chemotherapy for an otherwise healthy 55-year-old patient, and most (92%) were very or somewhat likely to recommend chemotherapy for an otherwise healthy 80-year-old patient. Fewer physicians (38%) were very likely to recommend chemotherapy for a 55-year-old patient with moderate congestive heart failure (CHF). Most physicians were very or somewhat unlikely to recommend chemotherapy for a patient with severe CHF, particularly if that patient was also 80 years old (92%).

View larger version (29K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 1. Likelihood of recommending adjuvant chemotherapy for a patient with stage III colon cancer. The colored vertical bars represent the proportion of physicians reporting they are very likely, somewhat likely, somewhat unlikely, or very unlikely to recommend adjuvant chemotherapy for hypothetical patients with stage III colon cancer who vary by patient age and comorbidity. Abbreviation: CHF, congestive heart failure.

In adjusted analyses, patient age and level of comorbidity were the strongest predictors of chemotherapy recommendation (Table 2). There was a significant interaction between patient age and comorbidity, indicating that physicians were less likely to recommend chemotherapy when patients were both older and sicker (P < .001). While nearly all physicians recommended chemotherapy for a 55-year-old patient with no comorbidity (99.0%), a 55-year-old patient with moderate congestive heart failure (88.6%), or an 80-year-old patient with no comorbidity (92.6%), many fewer would recommend chemotherapy for an 80-year-old patient with moderate (47.3%) or severe (8.9%) congestive heart failure.

We tested for additional interactions and found no association between patient comorbidity and physician age, teaching status, or cancer center or between patient age and physician age (all P .47). Teaching physicians (P = .001) and cancer-center physicians (P = .044) were more likely than their counterparts to recommend chemotherapy for older patients. We repeated analyses stratified by physician specialty (surgeons v medical oncologists) and results were similar (not shown).

	DISCUSSION

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In this large, geographically diverse survey of surgeons and medical oncologists we found that nearly all physicians would recommend adjuvant chemotherapy for an otherwise healthy 55-year-old man with stage III colon cancer, suggesting near unanimous agreement with clinical practice guidelines²⁵ recommending this therapy. Most were also likely to recommend chemotherapy for older patients who were healthy, but they were less likely to recommend chemotherapy for younger patients with severe comorbid illness or older patients with any comorbid illness, particularly if severe.

Prior research has demonstrated that many patients who are potentially eligible for adjuvant chemotherapy do not receive it.^11-13 Despite evidence that adjuvant chemotherapy benefits older patients as well as younger patients,⁷ numerous studies have shown that rates of chemotherapy decrease as patient age increases.^10-14 Because comorbidity increases as age increases, additional comorbidity may explain at least part of the decreasing use of chemotherapy with increasing age, although one study demonstrated decreasing chemotherapy with increasing age regardless of comorbidity.¹² The great majority of physicians in our study were likely to recommend chemotherapy for an 80-year-old patient who was healthy, although their recommendations were less strong than for a 55-year-old patient (Fig 1). Some physicians may be concerned about the potential for increased chemotherapy-related toxicity in the elderly (one study found an increased risk of leukopenia among older patients).⁷

Fewer physicians recommended chemotherapy for patients with significant comorbid illness, possibly because these patients may experience less benefit if their life expectancy is limited or because physicians are more concerned about toxicity. However, a recent study suggests that chemotherapy improves 5-year survival even among patients with heart failure and other chronic conditions.²⁶ We observed substantial variation in treatment recommendations for patients with comorbid illness (ie, for patients who were older with moderate comorbidity, approximately one half of physicians recommended chemotherapy while the other half recommended against it). This suggests that the individual physician a patient sees for care is an important factor in determining whether or not he or she receives chemotherapy. Such variability may reflect different approaches to making decisions in the absence of data or personal experiences with delivering chemotherapy. Clinical trials that include older patients and patients with comorbidity could be helpful to limit practice variation²⁷; until then, tools to help physicians estimate excess toxicity of chemotherapy among the elderly²⁸ may be useful. Development of tools to evaluate individual risks and benefits of chemotherapy are greatly needed.

Of the physician and practice characteristics we examined, only physician age was significantly associated with treatment recommendations, and teaching status and practicing in a cancer center were marginally associated with recommendations. Accounting for these factors explained only a small portion of the variation in recommendations. Physicians may differ in ways that we did not measure, such as how they perceive the relative risk/benefit ratios for patients who are older or have comorbid illness. They may also differ in their comfort level in treating complications of chemotherapy or managing comorbid conditions such as congestive heart failure in patients with cancer. Although our study did not address patients' preferences for chemotherapy, physicians' assessments of patients' preferences could be particularly important in decisions about adjuvant chemotherapy when there is uncertainty about the risks and benefits of therapy. Our findings also suggest that for patients desiring adjuvant chemotherapy, if one physician recommends against it, they may be able to find another who recommends for it by obtaining a second opinion.

The finding that older physicians (particularly those age 55 years) were less likely than younger physicians to recommend adjuvant chemotherapy is consistent with other literature suggesting that older physicians may be less likely than younger physicians to deliver guideline-recommended care.²⁹ Older physicians may have a more conservative practice style related to less recent oncology training. They may be less aware of recommendations, or they may be less comfortable than other physicians with generalizing clinical trial results to patients ineligible for the trials, such as older or sicker patients. Alternately, they may have had more experience with older or sicker patients not tolerating chemotherapy. Physicians with larger teaching roles and those working in cancer centers were also more likely to recommend chemotherapy (findings of borderline statistical significance); they may be the most up to date with the literature, or they may work in settings where support for patients with complications of chemotherapy is greatest. No other physician or practice characteristics were associated with treatment recommendations, and none of the physician characteristics were as strongly associated with recommendations as patient age or comorbidity. Interventions targeted to older physicians or those in nonteaching or non–cancer center settings or directing patients to younger physicians or cancer centers may increase rates of treatment for patients who are likely to benefit somewhat; however, such efforts are unlikely to have a major impact on rates of adjuvant chemotherapy use for patients with colon cancer because physician factors accounted for only a small portion of variation in recommendations.

Physician factors such as practice site, geographic setting, and financial incentives were not associated with treatment recommendations. Moreover, although tumor boards might help improve consistency of physician practice,³⁰ participation in tumor boards was not associated with recommendations for adjuvant chemotherapy. Surgeons, even though they do not typically prescribe chemotherapy, reported recommendations quite similar to medical oncologists.

Our study's strengths include a large, population-based cohort of cancer physicians from diverse geographic areas and a rich set of potentially relevant variables. However, our findings should be interpreted in light of several limitations. We assessed physicians' recommendations for treatment using vignettes; nevertheless, others have found clinical vignettes to be a valid tool for measuring care delivered in clinical practice.³¹ In future analyses, we can correlate physician reports of recommendations with the actual care that their patients received. The vignette patients represented only two ages and three levels of severity of a single comorbid illness, and responses may have differed if we had asked about different illnesses. Also, they did not include information about frailty, which some physicians may use to guide treatment recommendations.³² Still, comorbid illness is strongly related to frailty. The response option categories were by necessity somewhat artificial; however, our findings were robust to various ways of grouping responses. As CanCORS participants are not a nationally representative sample and our survey is subject to nonresponse bias, we cannot be certain that the physicians in our sample were representative of physicians caring for cancer patients nationally or in the regions studied. In addition, physicians' responses may have been influenced by social desirability bias if physicians perceived the correct response to be to recommend treatment. We did not specify flurouracil/leucovorin versus flurouracil/oxaliplatin regimens. Because the latter may now be preferred, especially in the elderly,^4-6 providing specific regimen details might have influenced responses.

In conclusion, most physicians agree with guidelines recommending adjuvant chemotherapy for stage III colon cancer in clinical situations for which evidence supports benefits. However, they differ widely on recommendations for patients who are sicker or older and sicker—settings for which clinical trial data on the relative benefits and risks of adjuvant chemotherapy are needed. Aside from physician age, teaching participation, and cancer center affiliation, no other physician or practice characteristics were associated with recommendations. Nevertheless, particularly for patients who are older and sicker, the specific physician seen for consultation regarding chemotherapy is a significant determinant of the likelihood of being treated. Understanding better the sources of variation not explained by patient age and comorbid illness may facilitate tailoring therapy to those patients most likely to benefit.

	AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

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The author(s) indicated no potential conflicts of interest.

	AUTHOR CONTRIBUTIONS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION AUTHORS' DISCLOSURES OF... AUTHOR CONTRIBUTIONS APPENDIX REFERENCES

 
Conception and design: Nancy L. Keating, Mary Beth Landrum, Carrie N. Klabunde, Robert H. Fletcher, Selwyn O. Rogers, William R. Doucette, Diana Tisnado, Steven Clauser, Katherine L. Kahn

Financial support: Nancy L. Keating

Collection and assembly of data: Nancy L. Keating, Mary Beth Landrum, Carrie N. Klabunde, Robert H. Fletcher, Selwyn O. Rogers, William R. Doucette, Diana Tisnado, Steven Clauser, Katherine L. Kahn

Data analysis and interpretation: Nancy L. Keating, Mary Beth Landrum, Carrie N. Klabunde, Robert H. Fletcher, Selwyn O. Rogers, William R. Doucette, Diana Tisnado, Steven Clauser, Katherine L. Kahn

Manuscript writing: Nancy L. Keating

Final approval of manuscript: Nancy L. Keating, Mary Beth Landrum, Carrie N. Klabunde, Robert H. Fletcher, Selwyn O. Rogers, William R. Doucette, Diana Tisnado, Steven Clauser, Katherine L. Kahn

	APPENDIX

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Appendix: Cancer Care Outcomes Research and Surveillance Physician Survey Development and Administration
Survey development. The Cancer Care Outcomes Research and Surveillance (CanCORS) physician survey was designed to collect information that can only be obtained reliably from physicians, including physicians' beliefs about treatments, physicians' style of practice, physicians' practice characteristics and financial arrangements, and physicians' demographics. When possible, items were taken (or adapted) from previously developed instruments. When items were not available from prior surveys, new questions were developed.

Five versions of the survey instrument were developed, each tailored to the type of physician who would be responding based on the role reported by the patient: (1) surgeons, (2) chemotherapy providers, (3) radiation therapy providers, (4) noncancer specialists caring for patients with colorectal cancer, and (5) noncancer specialists caring for patients with lung cancer. Where possible, questions on each version were identical. Some versions had additional questions specific to that discipline (eg, surgeons had questions specifically about volume of surgical operations).

The survey instruments underwent two rounds of cognitive testing by survey development staff at Westat, each followed by revisions to the instrument. In the first round of cognitive testing, 12 physicians from the Washington, DC, metropolitan area provided feedback about specific questions. After revisions to the questionnaire, 16 physicians from around the country completed the self-administered survey and then were interviewed by research staff. The survey instrument was revised to improve clarity and decrease the length. Questions were dropped if they were difficult to answer, were not likely to provide data with variation, or were of lower priority relative to the CanCORS synthesis document and analytic work plans.

Cohort. The target population of the provider survey was physicians who had important roles in the care of patient participants in CanCORS. The CanCORS patient cohort is a population-based cohort of individuals diagnosed with lung or colorectal cancer at one of the participating sites (eight counties in Northern California, Los Angeles County, the state of Iowa, the state of Alabama, 22 counties in central/eastern North Carolina, five integrated delivery systems, and 10 Veterans' Administration Medical Centers). Table A1 summarizes the cohorts of newly diagnosed patients who were ascertained and enrolled. CanCORS participants are similar to patients diagnosed with cancer in the United States as a whole (Catalano et al, unpublished manuscript).

In the patient survey, we identified physicians who played important roles in each patient's care, including physicians who discussed and/or provided surgery, chemotherapy, or radiation therapy, providers important in referring patients to surgeons (patients with lung cancer only), chemotherapy providers, or radiation providers, and providers most likely to know if the patient has a symptom. If a patient did not discuss surgery, chemotherapy, or radiation therapy with any providers, then we surveyed the doctor that they reported was most important in treatment decisions.

At one site (Veterans' Administration hospitals), the patient survey was not used to identify physicians. Rather, researchers identified all physicians with whom patients had interactions based on review of the inpatient and outpatient medical records. Because many patients had interactions with residents and fellows who were transiently at the VA hospitals, and because these trainees were working with attending physicians, only attending physicians are included in analyses.

Each site verified the names and contact information of physicians. Attempts were made to verify physicians' specialties to assure that the appropriate survey instrument be mailed to them. For example, if the doctor with whom a patient discussed surgery was actually their primary care doctor, then the physician would receive a survey instrument tailored to a noncancer specialist rather than one tailored to a surgeon.

Physicians who were mental health providers were ineligible for participation, consistent with the decision in CanCORS to not collect information about patients' mental health. If physicians had moved or retired, attempts were still made to contact those physicians, although such attempts were typically unsuccessful.

Survey administration procedures. Physicians were mailed a self-administered questionnaire. The questionnaire was accompanied by a cover letter printed on letterhead from the primary data collection site and was cosigned by the Director of the National Cancer Institute and the Medical Director of the American Cancer Society. Each packet also included one or more letters of endorsement matched to the recipient's specialty (including the American College of Surgeons, American Society of Clinical Oncologists, American Society of Therapeutic Radiology and Oncology, American Thoracic Society, American College of Chest Physicians, American Gastroenterological Association, American College of Physicians, and American Academy of Family Physicians).

Surveys were mailed by priority mail with a stamped, preaddressed return envelope. Physicians were also given the option of responding to the survey via a secure web site, after logging in with a username and password. Each survey was coded with a unique identifier to be used to link providers with patients and for follow-up of nonresponders. Three weeks after the initial mailing, another copy of the survey and cover letter was sent by first class mail to all nonresponders. Approximately 2 weeks later, a research assistant placed phone calls to the offices of nonresponding physicians to verify that the survey had been received, encourage physicians to complete and return it, and offer to mail or fax a replacement questionnaire. Up to 10 attempts were made to reach each nonresponding physician. After another 6 to 8 weeks, a third mailing of the survey and cover letter was sent to nonresponding physicians.

For each survey, the initial mailing included an incentive. At most sites, this incentive was in the form of a $20 check. At two sites, the incentive was a nonmonetary gift card with a $20 value. At the one site, this incentive was a $50 check incentive, due to the concern that $20 would not be sufficient compensation to positively influence survey response in this area. At a final site, a randomized trial of a $50 check or a $20 check incentive was conducted for the first 578 physicians; because of a significantly higher response rate, the remaining physicians received a $50 check (Keating et al, in press).

One Primary Data Collection and Research Center site made the initial contact with physicians by e-mail. In this case, the body of the e-mail included a brief message that mentioned the survey, described the attachments (cover letter and endorsement letter), included the URL to take the survey via the Internet, and noted that they will be receiving a mailing within the week that included a $20 check and a paper copy of the instrument.

The survey administration procedures were tested at each site using a run-in period during summer of 2004 where each site mailed the first 30 surveys. The remaining surveys were administered on a rolling basis during January 2005 through March 2007, although only 2% of the surveys were mailed after May 2006.

Data Entry
For web-based survey responses (13% of responses), data were entered directly into the Statistical Coordinating Center database from the web survey instrument. For paper survey responses, data were double entered by staff at each Primary Data Collection and Research Center site into a web version of the instrument specifically designed for data entry.

Response rates. We calculated absolute response rates and participation rates. The absolute response rate was defined as the response rate among all physicians who are believed to have cared for CanCORS patients. This includes a small number of physicians who are deceased or no longer in practice and physicians named by patients but whose sites were not able to identify valid contact information. The absolute response rate for the survey was 53.2%. The participation rate was defined as the response rate among physicians who cared for CanCORS patients, are not deceased or retired, and for whom sites were able to identify valid contact information. The overall participation rate was 61.0%. Absolute response rates and participation rates by site and physician characteristics are included in online-only Table A2.

Physicians in Northern California, Iowa, Los Angeles County, and those practicing in the Cancer Research Network managed care organizations were most likely to respond. Response rates did not differ by physician sex, but physicians who graduated from medical school in 1983 to 1989 were less likely than others to respond. Physicians providing radiation therapy were most likely to respond, and noncancer specialists caring for patients with colorectal cancer were least likely to respond.

	ACKNOWLEDGMENTS

 
We thank Yang Xu, MS, for expert programming assistance and Yulei He, PhD, for assistance with the multiple imputation.

	NOTES

 
This work of the Cancer Care Outcomes Research and Surveillance (CanCORS) Consortium was supported by grants from the National Cancer Institute (NCI) to the Statistical Coordinating Center (U01 CA093344) and the NCI-supported Primary Data Collection and Research Centers (Dana Farber Cancer Institute/Cancer Research Network U01 CA093332, Harvard Medical School/Northern California Cancer Center U01 CA093324, RAND/UCLA U01 CA093348, University of Alabama at Birmingham U01 CA093329, University of Iowa U01 CA01013, University of North Carolina U01 CA093326) and by a Department of Veteran's Affairs grant to the Durham VA Medical Center U01 CDA093344 (MOU) and HARQ 03-438MO-03).

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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Submitted December 21, 2007; accepted February 7, 2008.

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