Corticotroph Pituitary Carcinoma in a Patient With Lynch Syndrome (LS) and Pituitary Tumors in a Nationwide LS Cohort

Context: Lynch syndrome (LS) is a cancer-predisposing syndrome caused by germline mutations in genes involved in DNA mismatch repair (MMR). Patients are at high risk for several types of cancer, but pituitary tumors have not previously been reported. Case: A 51-year-old man with LS (MSH2 mutation) and a history of colon carcinoma presented with severe Cushing disease and a locally aggressive pituitary tumor. The tumor harbored a mutation consistent with the patient's germline mutation and displayed defect MMR function. Sixteen months later, the tumor had developed into a carcinoma with widespread liver metastases. The patient prompted us to perform a nationwide study in LS. Nationwide Study: A diagnosis consistent with a pituitary tumor was sought for in the Swedish National Patient Registry. In 910 patients with LS, representing all known cases in Sweden, another two clinically relevant pituitary tumors were found: an invasive nonsecreting macroadenoma and a microprolactinoma (i.e., in total three tumors vs. one expected). Conclusion: Germline mutations in MMR genes may contribute to the development and/or the clinical course of pituitary tumors. Because tumors with MMR mutations are susceptible to treatment with immune checkpoint inhibitors, we suggest to actively ask for a family history of LS in the workup of patients with aggressive pituitary tumors.