This symposium, largely devoted to colorectal cancer, has been organised as a tribute to the memory and legacy of Professor Ray McMahon. Ray passed away on Tuesday, 18 February 2025, after a short illness. He was 68. Ray was one of the most delightful and lovable characters in international pathology and had superb organisational, administrative and diplomatic skills, complemented by an extraordinarily friendly and humorous character.
There is little doubt that his greatest accomplishments were in his numerous roles in the International Academy of Pathology and the British Division of the IAP (BDIAP). He was elected to Council of the BDIAP in 1995 and served as its Treasurer for 12 years from 1996. A sure hand with economics and investments, Ray guaranteed the financial stability of the Society for all those years. He was President of the BDIAP from 2018 to 2020. He served with his typical proactive and yet diplomatic leadership and the Society is so much richer for his commitment and energy in these roles. He was elected Chair of the Finance Committee of the IAP, the world organisation, in 2012. This role he undertook for two years and then transferred to become the General Secretary of the IAP, a role that continued up until his sad demise, when he had just been elected as President-Elect of the IAP, a position that only two Pathologists working in the UK had previously held. Ms Sam Kiely, the BDIAP’s Managing Director and Assistant Secretary to the IAP, will discuss his various roles and his contributions to the IAP as part of this session.
In 2024, BDIAP Council ratified the establishment of the ‘Ray McMahon Lecture’, only the second named lecture that the Society has ever had, and he also became one of the very few who have been awarded both BDIAP Medals, only one of each being awarded each year: the Cunningham Medal for contributions to the BDIAP and the President’s Medal for contributions to international pathology education. These awards truly emphasise his massive contributions to pathology, the IAP and the BDIAP.

The serrated colorectal neoplasia pathway has become apparent over the last 30 years and is likely to account for 15-30% of cases of colorectal cancer (CRC). The spectrum of serrated polyps comprises the hyperplastic polyp (HP), the sessile serrated lesion (SSL) and the traditional serrated adenoma (TSA). HPs more commonly occur in the left colon, are particularly common in the rectum and carry negligible cancer risk. SSLs more commonly occur in the right colon, tend to be larger than HPs, are characterized e.g., by horizontal extension and basal dilatation of crypts and may harbour “conventional” dysplasia (SSLd). Some forms of “conventional” dysplasia within SSLd show loss of MLH-1 expression on immunohistochemistry. SSLs can be difficult to identify at endoscopy as they commonly occur on mucosal folds and may possess a mucin cap. TSAs more commonly occur in the left colon, are characterised e.g., by eosinophilic cytoplasm, pencillate nuclei and ectopic crypts and commonly harbour “conventional” dysplasia. HPs and SSLs typically contain BRAF mutations, while TSAs typically contain KRAS mutations, but may contain BRAF mutations if they develop from SSLs. Serrated polyps, apart from tiny rectal HPs, are associated with advanced colorectal neoplasia, including CRC. SSLs may grow slowly over several years, but the development of “conventional” dysplasia is associated with faster progression to CRC. CRC arising via the serrated pathway often show morphological features very similar to those arising via the adenoma-carcinoma sequence. However, they may alternatively show the features of “serrated” CRC e.g., mucinous growth, glandular serration and a low nuclear : cytoplasmic ratio. “Serrated” CRC comprise 10-15% of all CRC. Education programmes have helped endoscopists to identify serrated polyps (especially SSLs) and have helped histopathologists both to understand the significance of the serrated pathway and to recognise the spectrum of serrated lesions.