Clinicopathological importance of colorectal medullary carcinoma

Medullary carcinoma (MC) is a rare tumor with a solid growth pattern without glandular differentiation and constitutes less than 1% of colorectal cancers. Lymph node positivity and distant organ metastasis were reported to be lower than in other poorly differentiated adenocarcinomas. Therefore, the diagnosis of MC is pathologically important in terms of follow-up and treatment. We aimed to investigate the characteristics of medullary cancer in our case series.

427 patients with colorectal cancer (CRC) who underwent surgery between January 2011 and December 2017 were evaluated retrospectively in 2 groups as MC (n = 13) and non-MC (n = 414) in terms of demographic characteristics, pathological data, and oncological outcomes.

76.9% (n = 10) of the MC group were female while 36% (n = 149) of the non-MC group were female (p = 0.003). The tumors were located in the right colon in 84.6% (n = 11) of the MC patients and in 26.6% (n = 110) of the non-MC patients (p < 0.001). The rate of laparoscopy was 83.8% for all CRC patients, and 53.8% for the MC group (p = 0.01). T4 cases (69.2%) and tumor volume (131 ± 87 cm³) in the MC group were significantly higher than in the non-MC group (p < 0.05). The rate of high microsatellite instability (MSI) was 85%. 5‑year overall survival was 75% for the patients with MC and 82% for non-MC (p = 0.13).

MC is commonly localized in the right colon, has a large tumor size, and is mostly diagnosed in the T4 stage. As MC most likely have defects in DNA MMR, correct pathological diagnosis is important for postoperative treatment and the prognosis of the patients.