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Decision Analysis as an Aid to Determining the Management of Early Low Rectal Cancer for the Individual Patient

From the Department of Surgery and Public Health Sciences, Mount Sinai Hospital and University of Toronto, Mount Sinai Hospital Samuel Lunenfeld Research Unit; and Department of Medicine, Sunnybrook Hospital and University of Toronto, Toronto, Ontario, Canada.

Address reprint requests to Dr. R.S. McLeod, Suite 449, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, Canada M5G 1X5; Email rmcleod{at}mtsinai.on.ca

	ABSTRACT

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PURPOSE: Because there are no data available from randomized controlled trials (RCT), a decision analysis was performed to aid in the decision of which option, a local excision with or without radiotherapy or an abdominal perineal resection (APR), should be offered to medically fit patients with early (suspected T1/T2) low (< 5 cm) rectal cancer.

METHODS: All clinically relevant outcomes, including complications of surgery and radiotherapy, cure, salvageability after local recurrence, distant disease, and death, were modeled for both options. The probabilities of complications and outcomes after radiotherapy and/or local excision were derived from weighted averages of results from studies conducted between 1969 and 1997. The probabilities for the APR option were extracted from relevant RCTs. Long- and short-term patient-centered utilities for each complication and outcome were extracted from the literature and from expert opinion.

RESULTS: The expected utility of local excision (EU = 0.81) for the base case was higher than the expected utility for APR (EU = 0.78). Although the result was sensitive to all variables, local excision was always favored over APR within the plausible ranges of the variables taken one, two, or three at a time. The model illustrated the tension between the patient's perception of a colostomy and the higher recurrence rates with local excision.

CONCLUSION: The results of this decision analysis suggest that local therapy for early low rectal cancer is the preferred method of treatment. However, there must be careful preoperative assessment, patient selection, and consideration of patient concerns. In addition, decision analysis may be useful in providing patient information and assisting in decision making.

	INTRODUCTION

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COLORECTAL CANCER IS THE SECOND most common cancer in the United States.¹ One third of all colorectal cancers occur in the rectum. Despite potentially curative surgery, 30% to 50% of patients with colorectal cancer develop recurrences,² and one third of these patients die from the disease. Although advances in surgical technique and instruments have decreased the need for abdominal perineal resections (APR), APR is still considered to be the standard procedure for rectal cancers that are less than 5 cm above the anal verge.

Historically, patients with significant medical problems and/or patients who refused a colostomy were treated with local therapy. The recurrence and survival rates in these patients are better than expected in patients with early tumors (T1 to T3), so local excision has been offered as primary therapy in highly selected patients.³ The use of adjuvant radiotherapy and chemotherapy may contribute to the success of local excision. Thus, for early (T1/T2) low (< 5 cm from the anal verge) rectal cancer, which makes up approximately 8% of all rectal cancers, local excision may be an acceptable alternative to an APR when a sphincter-preserving procedure cannot be performed.

There are significant trade-offs between the surgical modalities. The rate of disease-free survival after treatment of rectal cancer may be higher after APR. In contrast, with local excision, gastrointestinal continence is maintained and there are fewer perioperative and long-term complications (eg, impotence and neurogenic bladder). In the absence of a randomized controlled trial comparing the two modalities, there is uncertainty as to whether an APR or local excision should be offered to medically fit patients with mobile early low rectal adenocarcinoma.

A decision analysis is an appropriate method to quantitate the relative value of these two surgical modalities in the management of rectal cancer.⁴ In our decision analysis, we attempted to answer the question of whether an abdominal perineal resection or local excision should be offered to medically fit patients with low (< 5 cm from the anal verge), mobile (on digital rectal examination), small (< 4 cm) adenocarcinoma of the rectum.

	METHODS

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Model Design
We used the SMLTREE computer program⁵ to model our decision analysis. SMLTREE requires that the clinical problem be illustrated as a decision tree.⁶ The two main branches of the tree represent the two surgical options: local excision and APR. The subbranches represent the clinical consequences of making the choice (Fig 1 -Fig 3). For example, if an APR is chosen, the patient may or may not suffer perioperative death. This later "chance event" was modeled as a dichotomous branch point in the decision tree (Fig 1). Other chance events, such as whether or not patients have a T3 lesion, were modeled as subsequent dichotomous branch points (Fig 1). Within the local excision arm, the need for an immediate APR, postoperative and/or radiotherapy complications, and stool incontinence were modeled (Fig 2). A common subtree was used to model the probability of local recurrence, metastatic disease, and salvageability for the different stages and therapy (Fig 3).

View larger version (16K): [in this window] [in a new window]   Fig 1. Tree structure for the APR arm. The APR option models the chance of postoperative death, the likelihood of "upstaging" a T1/T2 lesion to a T3 lesion, and the chance of radiotherapy complications with a T3 lesion.

View larger version (11K): [in this window] [in a new window]   Fig 3. Tree structure for the outcome subtree. The outcome subtree models the long-term events after treatment for rectal cancer: death from distant disease, recurrence, and the subsequent chance of salvage and cure.

View larger version (19K): [in this window] [in a new window]   Fig 2. Tree structure for the local excision arm. The local excision option models the chance of "upstaging" a T1/T2 lesion to a T3 lesion. It then models the treatment options and complications for T1 and T2 lesions.

Data and Assumptions
The probabilities were obtained from an extensive literature search. The probabilities for local excision and APR were extracted from studies that had similar patient characteristics. The probabilities and utilities used in this model are listed in Tables 1 and 2, respectively.

Patient selection.
It was assumed that patients who were considered candidates for local excision met specific criteria. After a thorough preoperative investigation, including a digital rectal examination and a transrectal ultrasound, the rectal tumor had to be mobile, less than 4 cm in size, less than 5 cm from the anal verge, free of nodal involvement, and not amenable to a low anterior resection. Patients were free of ulcerative colitis, had no significant family history of colorectal cancer, were medically fit, and were willing to undergo an APR and/or radiotherapy if necessary.

Conversion.
In this decision analysis, patients who received a local excision who were subsequently found to have a T3 lesion were modeled to have a subsequent APR. This treatment plan is substantiated in the literature.³⁰ Thus, a weighted mean conversion rate was calculated by taking the proportion of T3 lesions from each series that reported the frequency of T3 lesions among patients treated with local excision. The probability of dying and subsequent recurrence was considered to be equivalent to the probability after an immediate APR. This is substantiated in the literature.³¹

Proportion of T1 and T2 lesions.
The proportion of patients who had T1/T2 lesions was calculated for each reported series in which patients received a local excision as a cure. An overall average proportion of T1/T2 lesions was then calculated.

Operative complications.
Because the mortality rate after APR has been well reported, it was modeled. Because only one operative death after local excision has been reported in a series of patients accrued between 1948 and 1984,^13,32 mortality after local excision was not modeled in the decision analysis.

Perioperative complications modeled after local excision of T1 lesions included bleeding that required additional sutures, fistulas, and urinary tract infections. Because there were no reports of patients with T1 lesions treated without radiotherapy who required a temporary colostomy, this factor was not modeled. The probability of perioperative and radiotherapy complications was modeled for patients with locally excised T2 lesions and T3 lesions after APR.

Radiotherapy complications.
Postoperative radiotherapy was modeled for all patients with T3 lesions and patients with locally excised T2 lesions. Although numerous complications after local excision and radiotherapy (including proctitis, diarrhea, and skin rash) were reported, the need for a temporary colostomy was considered to be the most significant side effect and was the only complication modeled for patients with T2 lesions. Complications associated with radiotherapy after APR included bowel perforation and obstruction requiring subsequent surgery. These complications were added to the operative APR complications for T3 lesions.

Continence complications.
Some series reported that patients experienced night soiling and gas or fecal incontinence after radiotherapy for local excision. Regardless of severity, continence reported to be less than "good" was considered to be incontinence. No study reported the need for permanent colostomy in any of these patients.

Recurrence rates.
Studies that had a 5-year follow-up period were used to estimate the likelihood of recurrence. Data from a randomized controlled trial were used to estimate the recurrence rates for T1/T2 and T3 lesions after APR.^12,17 The recurrence rates for T1 and T2 lesions after local excision were extracted from series that had similar entry criteria and treatment for T1 (no radiotherapy) and T2 lesions (adjuvant radiotherapy). In the event that local recurrence was present with metastatic disease, the recurrence was considered to be distant only. Salvageability for local recurrence in patients initially treated with APR was estimated from one case series.¹⁹ Salvageability for patients treated with local excision was estimated by averaging the results from case series.

Utilities.
Utilities are a measure of the desirability that an individual or society has for a given long-term health state.⁴ Disutilities are "penalties" for short-term health states and have less impact on the overall quality of life. For instance, the disutilities associated with an APR include the short-term discomfort of recovery from the surgery, the negative impact of short-term complications, and the inconvenience of convalescence. In this model, the disutilities considered were those that occurred when the patient underwent initial or salvage surgery or radiotherapy, when recurrence was discovered, and when short-term complications caused by radiotherapy and/or surgery were experienced.

Long-term health states are measured in terms of utilities. Utilities may range from 0 to 1, with 0 representing death and 1 representing perfect health. Thus, the utility of perioperative death was 0. The utility of living with bladder dysfunction or impotence after an APR was based on utilities reported for patients who underwent radical prostatectomies.³³ The utility for fecal soilage after local excision and radiotherapy was considered to be more desirable than a permanent colostomy and was estimated from utilities reported for patients with ulcerative colitis who had had surgery.³⁴

The utility of life after a curative APR in this model captures only the quality of life with an ostomy. The utility of a patient with inoperable local or distant disease was thought to be independent of the original treatment and was extracted from utility data of medical patients with terminal disease.³⁵ Although death is inevitable, the long-term utility of life with metastasis was thought to be higher than the utility of perioperative death because for some period after surgery, a patient would have some quality of life.³⁶ The utility of life for a patient with an inoperable local recurrence was believed to be slightly lower than that for a patient with distant metastasis.

	RESULTS

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The expected utility for local excision (0.81) was higher than that for APR (0.78) in the baseline analysis. Thus, given the structure of the model and the baseline probability and utility values, local excision in the appropriately selected patients was the preferred surgical option.

Threshold analyses were performed to assess the robustness of the model (Table 3). Thus, the value of each variable in the model was changed to determine if and/or when an APR became the preferred surgical option. The utility of the local excision and APR options responded in the predicted manner. For instance, as the probability of a T2 lesion increased (and the probability of a T1 lesion decreased), the expected utility of the local excision option decreased. Table 3 shows the threshold values of each probability and utility when the APR option became the preferred surgical option. For most probabilities and utilities, local excision remained the preferred option, regardless of the value of the variable. There were only seven variables and four utilities for which an APR became the preferred option. However, for all of these, an APR became the preferred option outside the plausible range of values. For instance, if the rate of local recurrence after local excision of T1 lesions was greater than 23%, then an APR would be the preferred surgical option. According to the literature, the range (1% to 15%) for local recurrence of T1 lesions is much less than 23%, which suggests that within the plausible range of values, local excision is preferred. Therefore, local excision remained the preferred option, as was the case for the other 10 variables.

Two- and three-way sensitivity analyses were also performed to determine whether changing the values of two or three variables at the same time would result in a change in the preferred surgical option. Again, within plausible ranges of all variables, local excision remained the optimum choice. For instance, the three-way sensitivity analysis in Figure 4 illustrates the trade-offs between local recurrence after local excision and the quality of life with a colostomy. In the base case, we estimated that life with a colostomy has a utility of 0.95.³⁴ Thus, local excision would be preferred if the risk of a local recurrence after local excision of a T1 lesion was less than 20% or less than 18% after excision of a T2 lesion. However, if a patient is more adverse to a colostomy (for instance, with a utility of 0.85), then local excision would remain the preferred therapy if the risk of local recurrence after local excision of T1 and T2 lesions was less than 78% and 52%, respectively. Conversely, for patients who are adverse to any risk of local recurrence and would accept a colostomy (utility of 0.98), the preferred option would be an APR if the predicted local recurrence rates were greater than 6% and 5% for T1 and T2 lesions, respectively, after local excision.

View larger version (16K): [in this window] [in a new window]   Fig 4. Three-way sensitivity analysis demonstrates the trade-offs between local recurrence of locally excised T1 and T2 lesions and the utility of a colostomy (U*, utility of colostomy after an APR). The probability of T1 recurrence after local excision, T2 recurrence after local excision, and the utility of a colostomy were varied at the same time. The utility of colostomy affects the point where an APR is preferred over local excision when varying the range of T1 and T2 local recurrence rates after local excision.

	DISCUSSION

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For patients considered by the model, local excision tended to maximize the expected utility (average satisfaction) of patients. Thus, given that the assumptions inherent in the structure of the model are reasonable, local excision is the preferred method of managing early low rectal cancers. The probabilities and utilities used in this model were derived after an exhaustive review of the literature was performed. The expected utility of each option responded in an expected manner to variations in the prevalence of T1, T2, and T3 lesions, local recurrence rates, and the utilities associated with a permanent colostomy. With sensitivity analyses, the model suggested (1) that the implementation of the model within SMLTREE was correct and (2) that the superiority of local excision was robust to the uncertainty surrounding the probability and utility values within the model.

As with all decision analyses, one must be cautious with making definitive conclusions, especially because most data are not derived from randomized controlled trials (RCTs). This is particularly important in the local excision arm. For instance, authors report the results of local excision over a 10- to 15-year span during which surgical techniques and experience have likely changed and may have altered local recurrence rates. In addition, the results of series reported in the 1970s are likely to be different than results of series reported in the 1980s. Inasmuch as the surgical techniques have improved over time, the local recurrence rates may be biased against local excision. Thus, the utility of local excision may actually be higher than that in the base case. Nevertheless, we believe that varying the local recurrence rates of locally excised T1 and T2 lesions with one and two sensitivity analyses decreases the biases of retrospective data.

The model suggests that the expected utility for the local excision option is affected by the proportion of T1, T2, and T3 lesions. If all lesions are T1, local excision is favored. Conversely, the utility of a local excision decreases as the prevalence of T2 or T3 lesions increases. Thus, if physicians become less vigilant in their preoperative assessment, the utility of local excision will be less than that of an APR and harm would be done to patients. Similarly, if local excision were not adequate so that local recurrence rates were unacceptably high, an APR would be favored.

The role of radiotherapy in local treatment of early rectal cancer is likely important in this model. If all T1 lesions were treated with radiotherapy, the utility of the local excision arm would decrease and the APR arm might become the preferred option. In addition, there was no standard dose of radiotherapy given in the reported series, and complications seemed to be most frequent when doses were over 4500 cGy. Thus, the balance between the optimal therapeutic dose and the fewest complications is not known. Because the probability of complications after radiotherapy affects the utility of local excision, the benefits and risks of radiotherapy in local excision need to be better documented with data from RCTs or prospective cohort studies.

In order for the model to resemble usual clinical practice, the issue of salvageability was examined. However, regardless of the salvageability rate after an APR or local excision, local excision was preferred, probably because the proportion of patients with recurrence who were amenable to salvage surgery was too small to have an impact on the expected utilities of the two options. This was robust to changes in the recurrence rates of either the local excision or APR group.

This decision analysis suggests that with appropriate patient selection, local excision has a role in the management of early low rectal cancer. Although an RCT would be necessary to make definitive conclusions regarding one treatment option over another, it is unlikely that a local excision could be performed because cancers amenable to local excision are relatively rare. Furthermore, it is unlikely that patients would agree to participate in a trial in which surgical treatment would be determined by chance. Thus, this decision analysis aids in explicitly quantifying the considerations in determining treatment of low rectal cancer.

Perhaps the greatest value of this decision analysis is in its potential as a decision-making aid for patients. The three-way sensitivity analysis in Figure 4 illustrates the trade-offs between the risk of local recurrence and the perceived utility of living with a permanent colostomy. Given that there is variation in patient preferences, this model, coupled with individual ascertainment of utilities, could be used to discuss the risks involved with each option and determine the best treatment plan for an individual patient that considers the values of the patient. Thus, for patients who are adverse to a colostomy, local excision would remain the preferred option even if the risk of local recurrence is high. In contrast, for patients who would prefer an option that would be associated with the lowest risk of local recurrence, APR might be preferred. By explicitly considering all possible outcomes, assigning a probability for each of these variables, and determining the threshold where outcome would change, the decision analysis is more explicit than the usual clinical discussion around an issue.

Given the significant trade-offs between local excision and APR in the management of early low rectal cancer, a decision analysis is a useful technique for determining the most appropriate management. In addition, the potential for using decision analysis as a decision-making aid is clearly illustrated. Our analysis suggests that local excision for early low rectal cancer has more utility than an APR and that local excision may be considered an acceptable alternative to an APR in the management of early low rectal cancer.

	NOTES

 
Presented at the RCPSC Annual Meeting, Vancouver, BC, Canada, September 1997.

	REFERENCES

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

 
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Submitted June 24, 1998; accepted August 25, 1998.

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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 Temple, L. K.F. Articles by McLeod, R. S. Search for Related Content PubMed PubMed Citation Articles by Temple, L. K.F. Articles by McLeod, R. S. Social Bookmarking                            What's this?