Long-term outcomes following a pathological complete response at the primary tumor site after preoperative therapy in metastatic colorectal cancer.

[BACKGROUND] A pathological complete response (pCR) following neoadjuvant chemoradiation (CRT) is associated with a favorable prognosis in patients with locally advanced rectal cancer. Patients with metastatic colorectal cancer (mCRC) often receive systemic therapy, and some patients undergo primary tumor resection after preoperative therapy. However, whether oncological outcomes remain favorable in patients with mCRC and pCR in the primary tumor site (ypT0N0M1) following preoperative therapy is unknown.

[PATIENTS AND METHODS] Patients with mCRC who underwent preoperative therapy followed by primary tumor resection between March 2014 and August 2023, and in whom pCR was confirmed at the primary tumor site, were retrospectively included in this study. The outcome variables investigated were patient demographics, overall survival (OS), and progression-free survival (PFS).

[RESULTS] We included 57 patients who met the inclusion criteria. The median follow-up was 27.1 (range, 7.9-120.6) months. The 2-year PFS and 3-year OS rates in all the patients were 62.2% and 84.5%, respectively. Patients with a primary tumor site in the colon (n = 29) had superior OS (P = 0.039) and a trend toward superior PFS (P = .149) compared to those with a primary site in the rectum (n = 28).

[CONCLUSION] Patients with mCRC following preoperative therapy, particularly those with colon cancer, who experienced a pCR in the primary tumor site have a favorable prognosis.