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Adjuvant Chemotherapy Use for Medicare Beneficiaries With Stage II Colon Cancer

From the Department of Epidemiology and Biostatistics and Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY.

Address reprint requests to Deborah Schrag, MD, MPH, Health Outcomes Research Group, Department of Epidemiology and Biostatistics, Memorial-Sloan Kettering Cancer Center, 1275 York Ave, New York, NY 10021; email: schragd{at}mskcc.org

	ABSTRACT

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: Clinical trials have not demonstrated that adjuvant chemotherapy improves survival for patients with resected stage II colon cancer. Nevertheless, patients may receive this treatment despite its uncertain benefit. The objective of this study was to determine the extent to which adjuvant chemotherapy is used for patients with stage II colon cancer.

PATIENTS AND METHODS: Using the Surveillance, Epidemiology, and End Results-Medicare linked database, we identified 3,151 patients aged 65 to 75 with resected stage II colon cancer and no adverse prognostic features. The primary outcome was chemotherapy use within 3 months of surgery ascertained from claims submitted to Medicare. Relationships between patient characteristics and adjuvant chemotherapy use were measured and their significance was assessed using multivariable logistic regression. Survival for treated and untreated patients was compared using a Cox model.

RESULTS: Twenty-seven percent of patients received chemotherapy during the 3 postoperative months. Younger age at diagnosis, white race, unfavorable tumor grade, and low comorbidity were each associated with a greater likelihood of receiving treatment. Sex, the number of examined lymph nodes in the tumor specimen, the urgency of the surgical admission, and median income was each unrelated to treatment. Five-year survival was 75% for untreated patients and 78% for treated patients. After adjusting for known between-group differences, the hazard ratio for survival associated with adjuvant treatment was 0.91 (95% confidence interval, 0.77 to 1.09).

CONCLUSION: A substantial percentage of Medicare beneficiaries with resected stage II colon cancer receive adjuvant chemotherapy despite its uncertain benefit.

	INTRODUCTION

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USE OF ADJUVANT chemotherapy remains controversial for patients with stage II (T3N0M0 Dukes’ B2) colon cancer. Randomized trials have not demonstrated that treatment improves overall survival.^1-4 The most informative source of data comes from the International Multicentre Pooled Analysis of Colon Cancer Trials B2 investigators, who pooled data from 1,016 stage II patients treated on five randomized trials comparing fluorouracil-containing regimens to no treatment. They found that 5-year overall survival was 80% for untreated and 82% for treated patients, a difference that was not statistically significant.⁴ Unfortunately, no randomized trials have been large enough to exclude the possibility that adjuvant treatment provides a survival benefit in the single-digit range. A study would need to randomize 3,572 patients to detect a 4% survival difference between chemotherapy recipients and nonrecipients at 5 years with 80% power. Despite the persistent uncertainty regarding the benefit of adjuvant chemotherapy for stage II colon cancer, the clearly established survival benefit for patients with stage III tumors and evidence that treatment increases relapse-free survival have led some physicians to recommend adjuvant chemotherapy for their stage II patients. Clinical guidelines recommend that stage II patients consider participation in clinical trials, but there is continued debate regarding whether inclusion of a no-treatment control arm is appropriate.^5-7 A no-treatment arm is not included in a current cooperative group study.

To examine how physicians and cancer patients have interpreted the controversy regarding optimal treatment of stage II colon cancer, we measured chemotherapy use among Medicare beneficiaries with this diagnosis made in a Surveillance, Epidemiology, and End Results (SEER) region during the years 1991 to 1996. Our goal was to identify the clinical and demographic characteristics predictive of chemotherapy use and postoperative patterns of care. We also sought to compare clinical outcomes for treated and untreated patients, adjusting for known differences in these groups to the extent possible in the nonrandomized setting.

	PATIENTS AND METHODS

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Data Sources
Data from the SEER cancer registries and the Medicare claims files of the Health Care Financing Administration (HCFA) have been linked in order to facilitate population-based studies of the medical and economic outcomes of cancer treatment. The SEER registries, sponsored by the National Cancer Institute, ascertain all incident cancer cases diagnosed in five states and six United States metropolitan areas, representing approximately 14% of the United States population.⁸ The SEER program collects information on each incident cancer, including the primary site, histology classified according to the International Classification of Diseases for Oncology, 2nd edition schema (ICD-0 to 2),⁹ tumor stage at diagnosis, and patient demographics. Ninety-four percent of patients in the SEER registry aged 65 years or older have been successfully linked to their Medicare records.¹⁰

The Medicare program provides health insurance for 97% of the United States population aged 65 and older. The Medicare Provider Analysis and Review files provide details of all hospitalizations. For the 96% of Medicare beneficiaries who opt for part B coverage, claims for care delivered in hospital outpatient departments and physician’s offices are also recorded. In order to receive payment, health care providers submit medical claims coding diagnoses and procedures using the ICD, Ninth Revision (ICD-9) classification.

Cohort Definition
All patients aged 65 to 75 diagnosed with primary colon cancer in a SEER area during the years 1991 to 1996 and enrolled in parts A and B Medicare were potentially eligible for inclusion in our study. We excluded the 16% of patients enrolled in Medicare-managed care plans because these insurers were not required to submit detailed claims to the HCFA. Patients over the age of 75 were excluded from our analysis on the basis of a prior study indicating that few patients in this age bracket receive chemotherapy even in the setting of stage III disease.¹¹ Adenocarcinomas of the colon were defined using SEER codes for cancer site (18.0 to 18.9) and histology (8140, 8210-11, 8220-21, 8260-63, 8470, 8480-81, and 8490). Diagnoses noted exclusively on death certificates or at autopsy were excluded, as were those where the month of diagnosis or number of examined lymph nodes was unknown.

We searched Medicare claims records for patients who had colon cancer operations performed within 3 months of primary diagnosis and operations consistent with definitive tumor resection, according to the ICD-9, Clinical Modification classification (45.7x, 45.8, 48.4x, 48.5, and 48.6x). We identified patients with stage II disease using information on tumor size, nodal involvement, and distant spread recorded in the SEER database and classified according to the American Joint Committee on Cancer staging schema. Our analysis was restricted to patients who survived for at least 3 months after surgery because adjuvant therapy is not relevant for those who die in the immediate postoperative period. Patients diagnosed with a second malignancy other than skin cancer or a second colon primary tumor during this interval were also excluded.

Identification of Adjuvant Chemotherapy Use
Stage II patients who had at least one claim for chemotherapeutic treatment, administration, or agents in Medicare files at any point within the 3-month postoperative period were considered adjuvant therapy recipients. Medicare claims for medical evaluation for chemotherapy (ICD-9 codes V58.1, V66.2, and V67.2), chemotherapy administration (ICD-9 code 99.25; Current Procedural Terminology codes 96408, 96410, 96412, 96414, 96520, 96530, and 96545; Health Care Common Procedure Coding System codes Q0083 to Q0085; and revenue center codes 0331, 0332, and 0335), and intravenous chemotherapy agents (Health Care Common Procedure Coding System codes J9190, fluorouracil; J0640, leucovorin; and J9200, floxuridine) identified usage. Usage of experimental agents such as monoclonal antibody 17-1A could not be assessed because claims for experimental agents are not consistently submitted to Medicare for reimbursement.

Patient Characteristics Associated With Adjuvant Chemotherapy Use
Patient characteristics were evaluated on the basis of the information recorded in SEER-Medicare and included sex, race, the number of lymph nodes in the resected specimen, the year of diagnosis, the urgency of hospital admission, and the reporting SEER registry. Socioeconomic status was estimated on the basis of the median income in the patient’s census tract of residence.

To examine the effect of patient comorbidity on treatment rates, we used Romano’s modification of the Charlson comorbidity index.^12,13 The diagnoses included in the Charlson-Romano comorbidity index include myocardial infarction, diabetes, and moderate liver or renal failure and thus capture many of the absolute or relative contraindications to administration of adjuvant chemotherapy. We examined Medicare claims for the 15-month period extending from 12 months before the index surgical admission until 3 months postoperatively and assigned patients the maximal comorbidity observed.

Patients with adherent (T4) tumors, obstruction, or bowel perforation have a prognosis that more closely resembles that of stage III patients and, therefore, adjuvant chemotherapy use is often recommended.^14-16 Thus, we distinguished between patients with no adverse prognostic features and those with T4N0M0 tumors, obstruction, or perforation on the basis of the detailed staging information in the SEER registry (extent-of-disease codes 40, 45, 50, and 55) and diagnosis codes for obstruction (ICD codes 560.89 and 560.90) or perforation (ICD code 569.83) on Medicare claims. Only those with no adverse features are included in our primary analyses.

To better understand factors influencing adjuvant treatment decisions, we also measured the frequency of medical evaluations during the 3-month postoperative period using the specialty codes submitted on provider claims. Claims submitted by physicians who administer chemotherapy do not consistently identify their specialty as oncology but may instead use the more general code for internal medicine. Therefore, we distinguished between evaluations performed by any physician with either primary care or cancer expertise versus those performed by oncologists using unique physician identification numbers and HCFA specialty codes submitted on provider claims.

Statistical Analysis
We assessed the rates of chemotherapy use for patients grouped according to each clinical or demographic characteristic. In order to assess whether particular patient characteristics were independently associated with treatment, we used multivariable logistic regression to control for potential confounding by other variables. Characteristics associated with either treatment or survival were included in the regression model according to the categories listed in Table 1 with the exception of tumor registry, which was not included because of the multiple categories and small numbers of patients represented by some registries. Odds ratios for the receipt of chemotherapy compared to a referent category were calculated and adjusted for case mix.

View larger version (13K): [in this window] [in a new window]   Fig 1. Illustration of the survival for the 860 cohort members who received chemotherapy within 3 months of surgical resection (blue line) and the 2,291 who did not (red line).

	RESULTS

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For the 293 patients excluded from our cohort because of the presence of a T4 tumor or other adverse prognostic feature, the treatment rate was 33%. For patients excluded because their age at diagnosis was over 75, treatment rates were 16% for those aged 76 to 80 years and 7% for those aged 81 to 85 years.

Postoperative Medical Evaluations
Ninety-one percent of cohort members had at least one claim for an evaluation by a medical provider in the postoperative period. This rate was 98% for chemotherapy recipients and 90% for nonrecipients. Physician claims from a medical oncologist were submitted for 63% of recipients and 20% of nonrecipients. For the 994 cohort members who had a claim for a postoperative medical oncology consultation, 54% received adjuvant treatment and 46% did not.

Association Between Treatment and Survival
The Kaplan-Meier survival curves for the patients in the cohort are shown in Fig 1. Five-year survival was 75% for the 2,291 untreated patients and 78% for the 860 treated patients. The unadjusted risk ratio was 0.80 (95% confidence interval [CI], 0.68 to 0.95) but, after adjusting for known differences between the groups, the risk ratio was 0.91 (95% CI, 0.77 to 1.09). Propensity score analysis yielded similar results. To situate this risk ratio of 0.91 in context, we also calculated adjusted risk ratios for the association between other clinical characteristics and survival. Older age, male sex, black race, higher comorbidity, and urgency of hospital admission were each independently associated with worse survival. Neither chemotherapy treatment, nor the number of examined lymph nodes in the surgical specimen, nor the tumor grade, nor socioeconomic status, nor reporting registry was independently predictive of survival (Table 2).

	DISCUSSION

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Our stage II treatment rate of 27% contrasts with the 75% treatment rate for a parallel cohort of 65- to 75-year-olds with stage III colon cancers.¹¹ Similar to treatment patterns for patients with stage III disease, we found that age at diagnosis is strongly associated with treatment. Furthermore, this strong age trend suggests that an even larger proportion of patients under age 65 receive adjuvant chemotherapy. We were encouraged to note that sex and socioeconomic status appear to play no role in treatment decisions. As described for myriad medical conditions, blacks received treatment at substantially lower rates than whites.¹⁹ In contrast, treatment decisions do appear related to basic clinical and tumor characteristics. For example, higher levels of comorbidity and well-differentiated tumor histology were associated with lower treatment rates.

Retrospective comparison of treated and untreated patients in the nonrandomized setting is potentially flawed as a result of selection bias. Nonetheless, we proceeded to compare outcomes for treated and untreated patients because this clinical dilemma is encountered by approximately 26,000 colon cancer patients in the United States each year, and no randomized trial data are forthcoming over the short term. We selected a homogeneous cohort of stage II patients with similar age at diagnosis and no clearly identifiable adverse prognostic features and used both Cox modeling and propensity score analysis to minimize selection bias. We found that the survival curves for chemotherapy-treated and -untreated patients are superimposable for the first 3 postoperative years. Subsequently, survival is slightly superior for the chemotherapy-treated patients, with a 3% increment in 5-year survival that was nonsignificant in appropriately adjusted analyses. We emphasize the caveat that no firm conclusion can be drawn from nonrandomized data. Notably, our results are strikingly similar to results from randomized trials reported by the International Multicentre Pooled Analysis of Colon Cancer Trials B2 investigators.⁴ In their analysis with a median age of 62 (range, 22 to 86 years), survival was 80% for untreated and 82% for treated patients; whereas in our cohort with a median age of 69 (range, 65 to 75 years), survival was 75% for untreated and 78% for treated patients. Thus, if indeed there is any benefit to adjuvant chemotherapy for stage II disease, its absolute magnitude is likely to be small, less than a 6% absolute difference in 5-year survival. Because stage II colon cancer poses a frequently encountered clinical conundrum and commands significant health care resources, clinical trials that use molecular strategies in combination with innovative chemotherapy regimens should be developed and should include patients with stage II disease. However, we maintain that inclusion of a no-treatment arm in these trials remains justified. Although thousands of patients must be randomized and a long duration of follow-up is required to determine whether chemotherapy confers a small survival benefit in stage II disease, this effort would appear worthwhile, given that so many patients currently receive treatment of uncertain benefit in the off-protocol setting. Results of a clinical trial in stage II colon cancer would also have relevance for patients in the many countries where national health services effectively dictate what treatment patients are permitted to receive.

We found that both chemotherapy recipients and nonrecipients generally had an evaluation by a general internist and/or an oncologist in the immediate postoperative period and that these visits usually occurred in the outpatient setting. However, 63% of chemotherapy recipients and only 20% of nonrecipients had evidence of evaluation by an oncology subspecialist. Some oncologists are characterized according to their specialty (internal medicine) rather than their subspecialty in the Medicare claims, and this explains why 63% rather than 100% of chemotherapy recipients had evidence of an oncology consultation. Nevertheless, this pattern of postoperative evaluations yields several useful insights. First, the majority of patients who opt not to receive adjuvant therapy appear to make these decisions without input from an oncologist. Whether this is driven by surgeon or patient preferences cannot be ascertained from our data. Second, 54% of patients who had an evaluation by an oncologist received chemotherapy. It is noteworthy that, subsequent to consultation with the most knowledgeable subspecialists, so many elderly patients opt to receive an arduous treatment that has no clearly established survival benefit. This should lead us to carefully scrutinize the information that is communicated in these encounters, including such issues as whether survival benefit is addressed qualitatively or qualitatively. Although this high treatment rate may be attributable to patient preferences (patients who obtain oncology evaluations do so because they desire adjuvant treatment), it is more plausible that many United States oncologists actually endorse chemotherapy for their elderly stage II patients. This may be because oncologists genuinely believe that treatment confers a benefit. Economic motivations may also play a role. When surveyed, older patients have indicated that the primary determinant of their decisions regarding chemotherapy is physician advice.²⁰ However, ascertaining what really drives these decisions will require careful research that directly observes the patient-physician decision-making process.

Several additional limitations of our analysis must be noted. First, the potential for inaccurate coding exists for any claims-based analysis, and clinical information available from billing records is not as detailed as that available from chart review.^21-23 Chemotherapy may be underreported in Medicare claims, compromising the sensitivity of our approach to ascertaining treatment.^10,24 Second, our results may not generalize to the non-Medicare population or to the approximately 16% of Medicare beneficiaries who receive care in a health maintenance organization setting, where patterns of care may be different.²⁵ However, because two thirds of colon cancer patients are over 65 years of age and Medicare is the primary insurer for the vast majority, our study represents care received by typical United States patients.

Because fluorouracil treatment is generally well tolerated, physicians may perceive that young patients have little to lose by completing a course of adjuvant therapy and, because of their long life expectancy, potentially significant absolute gain from even a small incremental improvement in cure rate. However, the unwillingness of some clinicians to encourage their young patients to participate in a study with a no-treatment control arm would not make a randomized trial unfeasible because colon cancer is primarily a disease of the elderly. The major impediment to a trial evaluating the benefit of adjuvant chemotherapy compared to no treatment is practical. Accruing the necessary thousands of patients would require collaborative effort, consensus regarding the optimal treatment strategy, and long-term follow-up, because survival differences may only become manifest beyond 5 years. Despite these obstacles, the fact that 27% of the United States Medicare population with stage II colon cancer receives chemotherapy despite its uncertain benefit suggests that we are already devoting significant resources to this treatment strategy. Therefore, despite the size, costs, and long duration required to yield mature results, efforts to obtain a definitive answer to whether or not adjuvant chemotherapy is beneficial in stage II colon cancer are still warranted.

	ACKNOWLEDGMENTS

 
We thank the Applied Research Program, National Cancer Institute; the Office of Information Services, and the Office of Strategic Planning, HCFA; Information Management Services, Inc; and the SEER program tumor registries in the creation of the SEER-Medicare database. We thank Ramsey Tate for her editorial assistance.

	NOTES

 
This study used the linked Surveillance, Epidemiology, and End Results-Medicare database. The interpretation and reporting of these data are the sole responsibility of the authors.

	REFERENCES

TOP ABSTRACT INTRODUCTION PATIENTS AND METHODS RESULTS DISCUSSION REFERENCES

 
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Submitted November 19, 2001; accepted June 17, 2002.

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This Article Abstract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Save to my personal folders Download to citation manager Rights & Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Schrag, D. Articles by Begg, C. B. Search for Related Content PubMed PubMed Citation Articles by Schrag, D. Articles by Begg, C. B. Social Bookmarking                            What's this?