Colorectal signet-ring cell carcinoma: benefit from adjuvant chemotherapy but a poor prognostic factor

Colorectal signet-ring cell carcinoma (SRCC) has been associated with poor survival compared with mucinous adenocarcinoma (MC) and the more common adenocarcinoma (AC). Efficacy of adjuvant chemotherapy in SRCC has never been assessed. This study analyzes the prognostic impact of SRCC and determines whether colonic SRCC patients benefit from adjuvant chemotherapy equally compared with MC and AC patients. Data on 196,757 colorectal cancer (CRC) patients in the period 1989-2010 was included in this Dutch nationwide population-based study. Five-year relative survival estimates were calculated and multivariate relative survival analyses using a multiple regression model of relative excess risk (RER) were performed. SRCC was found in 1,972 (1.0%) patients. SRCC patients presented more frequently with stage III or IV disease than AC patients (75.2% vs. 43.6%, p < 0.0001) and SRCC was more frequently found in the proximal colon (57.7 vs. 32.0%, p < 0.0001). SRCC patients had a poor 5-year relative survival of 30.8% (95% CI 28.1-33.6%) in the colon and 19.5% (95% CI 14.7-24.8%) in the rectum compared with 56.8% (95% CI 56.4-57.1%) and 58.5% (95% CI 57.9-59.1%) for AC. This survival difference was found in stage II, but was most prominent in stage III. Compared with AC, there was no significant interaction between SRCC and adjuvant chemotherapy (RER 1.10, 95% CI 0.81-1.51), suggesting a comparable benefit from adjuvant chemotherapy in AC and SRCC. In conclusion, the prognostic impact of SRCC is dismal in both colon and rectal cancer patients, but adjuvant chemotherapy is associated with improved survival in AC, MC, and SRCC patients.