Abstract
Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide. We report a case of CRC in a man in his late 70s with hereditary haemochromatosis (HH) who historically required venesection two to three times per year to maintain target ferritin levels. Despite the absence of gastrointestinal symptoms or anaemia, his requirement for maintenance venesection unexpectedly ceased and ferritin levels remained low without treatment. Two faecal immunochemical tests were negative. Colonoscopy subsequently revealed an adenocarcinoma in the caecum. Chronic occult blood loss from the tumour likely counterbalanced the increased intestinal iron absorption characteristic of HH. This case highlights that an unexplained reduction in venesection requirements in HH may represent an early marker of occult gastrointestinal blood loss and should prompt consideration of further investigation.