Unusual case of colorectal carcinoma with sarcoid-like mediastinal adenopathy and near-fatal DPD deficiency

The liver is the commonest site for metastases in colorectal carcinoma; other isolated sites are considered extremely rare. 5-fluorouracil (5-FU) is the backbone of treatment for metastatic colorectal carcinoma (mCRC) and without it survival may be significantly reduced. It is primarily metabolised by dihydropyrimidine dehydrogenase (DPD). Testing for DPD deficiency is not a routine practice and toxicity will only manifest following drug challenge. There are limited standardised treatment guidelines in managing patients with severe drug reactions following 5-FU exposure. We describe a delayed presentation of life-threatening DPD deficiency in a patient with colorectal carcinoma and mediastinal lymphadenopathy. We describe our experience with chemotherapy in this difficult clinical scenario and highlight the importance of histological confirmation in unusual sites of metastatic disease.