Individuals are prone to develop cancers of the colon, genitourinary tract, and skin lesions, such as keratoacanthomas and sebaceous tumors.

[citation needed] Many patients who have sebaceous neoplasms with mutations in MSH2 and MLH1 do not in fact have Muir–Torre syndrome.

[9] In one study, a patient with defective MSH2 and MSH6 mismatch repair genes exhibited both syndromes.

This is the first case where a patient with genotypic changes consistent with HNPCC has been properly diagnosed with an overlap of both syndromes.

Sebaceous neoplasms are only infrequently encountered, and immunohistochemistry is reliable and readily available, so researchers have recommended its use.

This includes frequent and early colonoscopies, mammograms, dermatologic evaluation, and imaging of the abdomen and pelvis.

A British physician and surgeon, Muir noted a patient with many keratoacanthomas who went on to develop several internal malignancies at a young age in the 1960s.