Increased expression of calpain 6 in uterine sarcomas and carcinosarcomas: an immunohistochemical analysis

Calpain 6 (Capn6) is one of the calcium-dependent intracellular nonlysosomal proteases. Recently, Capn6 was found to be overexpressed in leiomyosarcomas (LMSs) compared with normal myometrium. This investigation was performed to determine the expression of Capn6 in uterine sarcomas and carcinosarcomas and to determine whether there is a relationship between the clinical findings and the expression of Capn6. Seventeen cases, treated from 1994 to 2004, were evaluated. These included five LMS, seven endometrial stromal sarcomas, and five uterine carcinosarcomas (malignant mullerian mixed tumor [MMMT]). Formalin-fixed, paraffin-embedded tissue sections were immunostained with anti-Capn6 domain-II (anti-DII) and anti-Capn6 domain-T (anti-DT) antibodies. A semiquantitative assessment was performed. All 17 tumors expressed the Capn6 protein; this finding was in contrast to the absence of expression of the Capn6 protein in all of the normal control tissues. The distribution of staining was diffuse. The cytoplasm and nucleus were stained evenly. The mean age of the patients whose samples were stained strongly by anti-DII was higher (P = 0.031). There were no significant associations between tumor stage and staining intensity by anti-DII (P = 1.000) or anti-DT (P = 0.576). However, there was a marginally significant association between tumor subtype and staining intensity (P = 0.054 and P = 0.053, respectively). The expression of Capn6 had no association with disease-free survival (P = 0.367 and P = 0.166, respectively). All of the uterine sarcomas and MMMTs expressed Capn6 protein. This study showed that there were marginally significant associations between tumor subtypes and staining intensity, but no association was found with tumor stage and survival.