Almost all patients were women with tumors in the cecum or proximal digestive tract. months, with NGI-1 a 5-year overall survival of 42. 9% for MCs and 76. 6% intended for PDAs (p= 0. 048). Univariate analysis found local recurrence (p= 0. 001) and medullary subtype (p= 0. 043) associated with reduce survival. == Conclusions == Medullary carcinomas were of greater tumor size and associated with more LVI and worse survival versus PDAs with MSI in stage III. Keywords: colorectal, cancer, microsatellite instability, medullary carcinoma, survival == Introduction == Colorectal medullary carcinoma (MC) is a unique, poorly differentiated adenocarcinoma (PDA) increasingly identified and analyzed in the last two decades. Formerly known as large cell adenocarcinoma with minimal differentiation, it is now being referred to as medullary carcinoma because of its organoid structures that is just like the pattern seen in developing embryonic organs [1]. However , it is important not to use this term in the colorectal literature with all the same connotation as it is utilized in breast and thyroid, because the clinicopathological features are quite diverse. Medullary carcinoma has been included as a distinct histological type in the World Wellness Organization (WHO) classification of colorectal carcinomas, wherein it is described as being characterized by linens of malignant cells with vesicular nuclei, and prominent nucleoli, along with prominent intraepithelial lymphocytic infiltrate [2]. The MC is a solid variety of adenocarcinoma with very little glandular differentiation. Although they are morphologically similar to undifferentiated adenocarcinoma (UDA), they tend to display distinct clinical behavior: they are typically more common in old females, less likely to present with nodal involvement and generally possess a better prognosis [3]. However , there are very few data published in this respect. Another characteristic feature of MC is its strong association with microsatellite instability NGI-1 (MSI) in at least 60% of cases [4, 5]. Most colorectal carcinomas are adenocarcinomas of conventional type (adenocarcinoma NOS, not otherwise specified). Adenocarcinomas are graded into well-differentiated, moderately differentiated, poorly differentiated and undifferentiated tumors (grades 1, 2, 3 and 4, respectively) depending on the proportion of gland formation in the least differentiated component of the tumor away from the invasive edge, according to the WHO criteria. This is a subjective evaluation with low levels of agreement among pathologists [6], but histologic grading has been shown KRT4 to be an independent prognostic element for colorectal carcinoma, particularly true intended for the poorly differentiated subgroup [710]. The WHO ALSO and the American Joint Committee on Cancer (AJCC) recommend a 2-tiered histologic grading system: low grade intended for well-differentiated and moderately differentiated adenocarcinomas (50100% gland NGI-1 formation) and high grade for poorly differentiated adenocarcinomas (049% gland formation) and undifferentiated adenocarcinoma (01% gland formation) [11]. Screening tumors intended for microsatellite instability (MSI) by immunohistochemistry intended for mismatch repair (MMR) proteins MLH1, MSH2, PMS2, and MSH6 and/or by molecular based methods is routinely performed intended for patients diagnosed with colorectal carcinoma, primarily to screen intended for Lynch syndrome and because of it has been reported to be a strong positive prognostic factor [1215]. NGI-1 Up to 15% of all colorectal carcinomas demonstrate MSI; the rest are called microsatellite stable (MSS) carcinomas. Some histologic subtypes of colorectal carcinomas are more commonly observed in MSI tumors, including medullary carcinomas, mucinous adenocarcinomas, and signet ring cell carcinomas [16]. The adverse prognosis associated with the poor differentiation of most of these tumor subtypes contrasts with the positive prognosis associated with MSI. Consequently, the current WHO ALSO histologic grading does not apply to colorectal MC. == Aim == According to the few released series and data about survival and prognosis of this tumor, and to further characterize the clinicopathologic attributes and survival of MCs, the present study compares the morphological and behavioral features of MCs with MSI with those of poorly differentiated NGI-1 cases of conventional adenocarcinomas (PDA) matched for clinical stage (AJCC stage III) and MSI. == Material and methods == We searched in.