Microsatellite instability and immunostaining for MSH‐2 and MLH‐1 in cutaneous and internal tumors from patients with the Muir–Torre syndrome

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Abstract
Background:  Muir‐Torre syndrome (MTS) is characterized by the co‐existence of sebaceous gland tumors of the skin and internal malignancies. Currently, MTS is regarded as a variant of the hereditary non‐polyposis colon cancer syndrome (HNPCC). Both MTS and HNPCC are secondary to germline mutations in DNA mismatch repair genes (mainly MSH‐2 and MLH‐1).Methods:  Cutaneous (eight sebaceous adenomas, one sebaceous carcinoma and one keratoacanthoma) and internal tumors (four colonic adenocarcinomas, two endometrial carcinomas, two transitional cell carcinomas of renal pelvis and ureter, one adenocarcinoma of the small bowel, one ovarian carcinoma and one colonic tubular adenoma) were obtained from six patients with MTS and were subjected to microsatellite instability (MI) analysis, and to immunostaining for MLH‐1 and MSH‐2. MI was assessed by evaluating three (CA)n dinucleotide repeats (D2S123, D5S346, D17S250) and the mononucleotide tracts BAT 26 and BAT 25.Results:  All cutaneous and internal tumors exhibited MI. An immunohistochemical concordance between all tumors within each single patient was obtained in five cases. In these five patients all tumors exhibited a lack of MSH‐2 staining, consistent with a germline abnormality in this gene. In the one remaining case, the immunohistochemical staining in the sebaceous adenoma was negative for MLH‐1 and positive for MSH‐2, consistent with a germline alteration in MLH‐1. However, the colonic adenocarcinoma in that patient showed positivity for MSH‐2 and an equivocal positivity for MLH‐1.Conclusions: The results confirm that tumors from patients with MTS exhibit MI. Moreover, immunostaining for MLH‐1 and MSH‐2 may be useful to identify the most probable gene responsible for the disease in each family.