MMR status in prostate cancer differed between foci in over half of multi-block cases

The edition in brief

In 32 treatment-naive mismatch repair-deficient prostate cancers from one institution, MMR immunohistochemistry on multiple blocks in 14 cases showed discordant status between foci in 8 (57%), with deficiency always confined to the highest-grade focus. Most losses were MSH2/MSH6, cribriform or intraductal pattern was present in 78%, and a third of those germline-tested had Lynch syndrome. FOG1 immunohistochemistry was moderate to high in 91.1% of gastric and oesophageal adenocarcinomas, where CDX2 was negative to low in 51.3%; it was absent in oesophageal squamous carcinoma and negative to low in 92.9% of colonic adenocarcinomas, though present in some pancreatic and ampullary cancers. In 23 paediatric tumours profiled on both Oxford Nanopore and Illumina EPIC arrays, nanopore classification agreed with integrated histology at family level in all CNS cases, MGMT status matched in 16 of 17, and the pan-cancer model performed poorly outside the CNS. A comparison of 15 metaplastic breast carcinomas with squamous differentiation and 18 cutaneous SCCs of breast and chest skin found CK7, SOX10 and TRPS1 more frequent in breast primaries, PIK3CA alterations in breast and NOTCH1 mutations and UV signatures only in skin.