Despite marked recent advances in chemotherapy, few reports have addressed the prognosis for mCRC patients achieving CR. Despite the small sample size, the results of this study are significant for understanding the clinical course of the patients achieving CR. Clinical outcomes were evaluated for 23 CRC patients confirmed CR to systematic chemotherapy. Results showed that patients with CR to chemotherapy had a high probability of disease progression, but a relatively long-term prognosis.
Although CR determined imaging is a useful criterion for evaluating the efficiency of chemotherapy, some liver metastasis studies have reported a discrepancy between CR visualized by imaging versus pathologically confirmed CR. Approximately 20–25% of liver metastases disappear after systemic chemotherapy; among such disappearing liver metastasis (DLM), “true CR” has been reported in 33–83% of cases. Therefore, resection is recommended for DLM after chemotherapy.[13–16] In the present study, 17 (73.9%) patients with CR to systematic chemotherapy had disease progression after a median follow-up duration of 48.1 months. Another study also reported that 84% of patients with CR had disease progression. These data indicate a discrepancy between CR determined by imaging and actual complete clearance of cancer in other organs.
Use of maintenance chemotherapy after achievement of CR is unclear. Research has shown negative results for maintenance chemotherapy after achievement of CR. Dy GK et al compared OS in 22 of 62 patients with CR with <2 cycles of maintenance chemotherapy and 40 patients with >2 cycles of chemotherapy in 2007. As a result, OS from CR was 39.8 months and 29.2 months, respectively; maintenance chemotherapy did not prolong OS. However, the therapeutic background for the 2007 study differs from the present context. Treatment strategies after achievement of CR have not been established; the approach should be based on the high potential for tumor cells to remain even after CR. Furthermore, the OPTIMOX2 study, which compared chemotherapy discontinuation with maintenance therapy, indicated that planned complete discontinuation of chemotherapy had a negative impact on duration of disease control and PFS versus the maintenance therapy strategy. Therefore, in the present study, maintenance chemotherapy was continued until disease progression or for 6–12 months after CR, except for cases in which pathological CR was confirmed after surgery for DLM. Median duration of maintenance chemotherapy was 11.1 months.
In the present study, median PFS was 26.6 months and median OS was 91.7 months, which exceeds the PFS (15.4 months) and OS (44.3 months) in the 2007 study. These more recent findings indicate that advances in chemotherapy have improved the prognosis of patients with CR; however, direct comparison with the 2007 study is difficult results because of different therapeutic backgrounds, and the recent data do not demonstrate a negative impact for continuing maintenance chemotherapy after CR.
This study has some limitations. First, a relatively small patient sample was derived from a single institution. Second, systematic chemotherapy regimens were not uniformly introduced, which result in treatment bias.