42. Lymph node negative colorectal adenocarcinomas with distant metastases have distinct morphological features

Abstract

Background In the neoplastic progression of colorectal adenocarcinoma (CRC), lymph node metastasis are generally considered to precede distant metastases and the AJCC staging for CRC reflects this. Occasionally, however, CRC develops distant metastasis without identifiable lymph node metastasis. This group of carcinomas has been infrequently studied. Aims To determine whether clinical and morphological differences exist between CRC with distant but not lymph nodes metastases and (1) CRC with both lymph node and distant metastases and (2) CRC with neither lymph node nor distant metastases. Methods A retrospective review was undertaken of CRC resection cases reported at Envoi Specialist Pathologists in 2 calendar years (2011–2012). CRC with distant but not lymph node metastasis (N0M1) ( n = 17) were compared with CRC with both lymph node and distant metastasis (N + M1; n = 60) and adenocarcinomas with neither lymph node nor distant metastasis (N0M0; n = 421). Features evaluated were: gender, age, site, tumour size, tumour budding, venous invasion, tumour grade, mismatch repair protein status and number of lymph nodes retrieved in the resection specimens. Results and conclusions N0M1 CRC were more likely to be lower grade than N + M1 CRC (83 vs 58.3% low grade; p = 0.002). When compared with N0M0 carcinomas, N0M1 carcinomas were more likely to occur in younger patients (62.9 vs 69.6 years; p = 0.045) and to exhibit tumour budding (70.6% vs 35.9%; p = 0.005) and vascular (lymphatic and venous) invasion (58.8% vs 21.3%; p = 0.001). These findings suggest that N0M1 CRC has distinct morphological features. This may be the result of distinct intrinsic properties (e.g., genetic subtype) that favour distant metastasis. The adverse significance of tumour budding and vascular invasion is further highlighted by this study.