Prognosis of Signet Ring Cell Carcinoma of the Colon and Rectum and their Distinction of Mucinous Adenocarcinoma with Signet Ring Cells. A Comparative Study.

Signet ring cell carcinoma (SRCC) of the colorectum is very rare, comprising between <1% and 2.4% cases of colorectal cancer. Patients' prognoses are poor. Several case reports had described as SRCC cases that are mucinous adenocarcinomas (MAC) with signet ring cells (SRC). In order to clearly delineate between MAC with SRC and SRCC, we performed a retrospective study at a national cancer referral center in which survival and clinicopathological characteristics between these two forms were compared and also SRCC were characterized by immunohistochemistry. We retrieved 32 cases that had been classified as either SRCC or MAC with SRC subtypes. It was noted that SRCC patients presented at older ages, demonstrated more advanced clinical stages, lymphovascular invasion, lymph node metastases, and higher carcinoembrionic levels than MAC with SRC patients. Regarding SRCC immunophenotype, 50% showed loss of CDX2 expression, 33% were CK20 negative, 41.7% were CK7 positive, and 25% were negative for both CK7 and CK20. For the MAC with SRC and SRCC groups, the median disease-specific survival (DSS) was 46.1 months (95% CI 36.9-55.25) and 22.4 months (95% CI 5.1-39.7 [p = 0.039]), respectively. The 3-year DSS was 80.7% and 28.6% (p = 0.017) for the MAC and SRCC patients, respectively. Univariate and multivariate analyses showed that SRCC was associated with decreased survival. SRCC had several clinicopathological features that permitted differentiation of MAC with SRC from SRCC patients, who had a poor DSS. A differential diagnosis for metastatic gastric cancer is only possible with a good clinicopathological correlation.