Relations of changes in serum carcinoembryonic antigen (CEA) levels before and after chemoradiotherapy (CRT) and after surgery to histological response and outcomes in patients with locally advanced rectal cancer (LARC)

804 Background: Multidisciplinary treatment had been a standard of care for locally advanced rectal cancer. Serum CEA had been reported as one of the predictive factors to CRT, however, serum CEA levels may change after CRT and surgery. We examined the relations of serum CEA before CRT, after CRT, and after surgery to histological response and outcomes. Methods: The subjects were 149 patients with cStage II or III adenocarcinoma of the rectum who underwent surgery after CRT from 2005 through 2013. A total dose of 40 to 45 Gy with concurrent oral UFT or S-1 was delivered. Surgery was performed 6 to 8 weeks after CRT. A serum CEA > 5 ng/mL was defined as positive. Patients with negative serum CEA before CRT were designated as group 1. Patients with positive serum CEA before CRT that became negative after CRT were designated as group 2. Patients with positive serum CEA after CRT that became negative after surgery were designated as group 3, and patients with positive serum CEA after CRT as well as after surgery were designated as group 4. The median follow-up period of the survivors was 60.4 months. Results: The numbers of patients in Groups 1, 2, 3, and 4 were 55 (37%), 41 (28%), 37 (25%), and 16 (11%), respectively. The incidences of pCR, T downstaging, and N downstaging did not differ significantly among the groups (p = 0.094, 0.060, and 0.346). Rates of marked regression (TRG Grade 1 or 2) were 55% in Group 1, 42% in Group 2, 16% in Group 3, 25% in group 4. The rates were significantly higher in groups 1 and 2 (p = 0.001).5y DFS was 76% in group 1, 75% in group 2, 77% in group 3, and 48% in group 4 and was significantly lower in group 4 (p = 0.024). 5y OS was 88% in group 1, 91% in group 2, 85% in group 3, and 68% in group 4 and was significantly lower in group 4 than that in groups 1 and 2 (p = 0.03, 0.019). Conclusions: In patients with rectal cancer who received CRT, changes in serum CEA levels before and after CRT and after surgery were intimately related to the histological response of the primary lesion. Patients who continued to have positive serum CEA levels after surgery had poor outcomes, strongly suggesting the presence of occult distant metastasis.