While genetic testing is mandatory whenever the familial form of MTC is suspected, germline RET testing may also be recommended in all patients with newly diagnosed C cell hyperplasia (CCH) or apparently sporadic MTC, since approximately 7% of patients, who would appear to have a “sporadic” form, in truth have an unsuspected germline variant in the RET proto-oncogene. Here, RET is linked to C-cell hyperplasia.