Postoperative adjuvant chemotherapy in rectal cancer operated for cure.

BACKGROUND

Colorectal cancer is one of the most common types of cancer in the Western world. Apart from surgery - which remains the mainstay of treatment for resectable primary tumours - postoperative (i.e., adjuvant) chemotherapy with 5-fluorouracil (5-FU) based regimens is now the standard treatment in Dukes' C (TNM stage III) colon tumours i.e. tumours with metastases in the regional lymph nodes but no distant metastases. In contrast, the evidence for recommendations of adjuvant therapy in rectal cancer is sparse. In Europe it is generally acknowledged that locally advanced rectal tumours receive preoperative (i.e., neoadjuvant) downstaging by radiotherapy (or chemoradiotion), whereas in the US postoperative chemoradiotion is considered the treatment of choice in all Dukes' C rectal cancers. Overall, no universal consensus exists on the adjuvant treatment of surgically resectable rectal carcinoma; moreover, no formal systematic review and meta-analysis has been so far performed on this subject.

OBJECTIVES

We undertook a systematic review of the scientific literature from 1975 until March 2011 in order to quantitatively summarize the available evidence regarding the impact of postoperative adjuvant chemotherapy on the survival of patients with surgically resectable rectal cancer. The outcomes of interest were overall survival (OS) and disease-free survival (DFS).

SEARCH METHODS

CCCG standard search strategy in defined databases with the following supplementary search. 1. Rect* or colorect* - 2. Cancer or carcinom* or adenocarc* or neoplasm* or tumour - 3. Adjuv* - 4. Chemother* - 5. Postoper*

SELECTION CRITERIA

Randomised controlled trials (RCT) comparing patients undergoing surgery for rectal cancer who received no adjuvant chemotherapy with those receiving any postoperative chemotherapy regimen.

DATA COLLECTION AND ANALYSIS

Two authors extracted data and a third author performed an independent search for verification. The main outcome measure was the hazard ratio (HR) between the risk of event between the treatment arm (adjuvant chemotherapy) and the control arm (no adjuvant chemotherapy). The survival data were either entered directly in RevMan or extrapolated from Kaplan-Meier plots and then entered in RevMan. Due to expected clinical heterogeneity a random effects model was used for creating the pooled estimates of treatment efficacy.

MAIN RESULTS

A total of 21 eligible RCTs were identified and used for meta-analysis purposes. Overall, 16,215 patients with colorectal cancer were enrolled, 9,785 being affected with rectal carcinoma. Considering patients with rectal cancer only, 4,854 cases were randomized to receive potentially curative surgery of the primary tumour plus adjuvant chemotherapy and 4,367 to receive surgery plus observation. The mean number of patients enrolled was 466 (range: 54-1,243 cases). 11 RCTs had been performed in Western countries and 10 in Japan. All trials used fluoropyrimidine-based chemotherapy (no modern drugs - such as oxaliplatin, irinotecan or biological agents - were tested).Overall survival (OS) data were available in 21 RCTs and the data available for meta-analysis regarded 9,221 patients: of these, 4854 patients were randomized to adjuvant chemotherapy (treatment arm) and 4,367 patients did not receive adjuvant chemotherapy (control arm). The meta-analysis of these RCTs showed a significant reduction in the risk of death (17%) among patients undergoing postoperative chemotherapy as compared to those undergoing observation (HR=0.83, CI: 0.76-0.91). Between-study heterogeneity was moderate (I-squared=30%) but significant (P=0.09) at the 10% alpha level.Disease-free survival (DFS) data were reported in 20 RCTs, and the data suitable for meta-analysis included 8,530 patients. Of these, 4,515 patients were randomized to postoperative chemotherapy (treatment arm) and 4,015 patients received no postoperative chemotherapy (control arm). The meta-analysis of these RCTs showed a reduction in the risk of disease recurrence (25%) among patients undergoing adjuvant chemotherapy as compared to those undergoing observation (HR=0.75, CI: 0.68-0.83). Between-study heterogeneity was moderate (I-squared=41%) but significant (P=0.03).While analyzing both OS and DFS data, sensitivity analyses did not find any difference in treatment effect based on trial sample size or geographical region (Western vs Japanese). Available data were insufficient to investigate on the effect of adjuvant chemotherapy separately in different TNM stages in terms of both OS and DFS. No plausible source of heterogeneity was formally identified, although variability in treatment regimens and TNM stages of enrolled patients might have played a significant role in the difference of reported results.

AUTHORS' CONCLUSIONS: The results of this meta-analysis support the use of 5-FU based postoperative adjuvant chemotherapy for patients undergoing apparently radical surgery for non-metastatic rectal carcinoma. Available data do not allow us to define whether the efficacy of this treatment is highest in one specific TNM stage. The implementation of modern anti-cancer agents in the adjuvant setting is warranted to improve the results shown by this meta-analysis. Randomized trials of adjuvant chemotherapy for patients receiving preoperative neoadjuvant therapy are also needed in order to define the role of postoperative chemotherapy in the multimodal treatment of resectable rectal cancer.