Diagnostic implications of Ki-67 expression in adipocytes and lipoblasts: an immunohistochemical study

Ki-67 expression is an important tool for distinguishing between malignant and benign tumors. It usually shows the nuclear staining. However, the cell membrane staining of MIB-1, which is one of the clones of Ki-67, in the hyalinizing trabecular adenoma of the thyroid gland and other tumors had also been reported. In our practice, we found that the 7B11 antibody could be immunoreactived with the adipose tissues inside or around tumors in the membrane. Thus, in this study, we determined if Ki-67 expression would be useful in recognizing the lipoblasts and adipocytes. The five clones of the Ki-67 antibody, namely, 7B11, K-2, SP5, MIB-1, and SP6 were selected. The adipocytes showed strong 7B11 staining in the cell membrane. The brown fat cells were strongly immunoreactive with 7B11 in the arachnoid layer of the cytoplasm. The adipocytes and brown fat cells showed positive, albeit weaker K-2 staining in the cell membrane and cytoplasm, respectively, compared to 7B11. The adipose tissues and brown fat cells were non-reactive to clones SP5, MIB-1, and SP6. All adipocytes in the lipomas, angiolipomas, uterine lipoleiomyomas, and angioleiomyolipomas showed diffusedly positive 7B11 and K-2 staining in the cell membrane, with stronger immunoreactivity to 7B11 compared with K-2. All hibernomas showed diffusedly cytoplasmic arachnoid staining of 7B11, but only focal to K-2. The lipoblasts in adipocytic tumors also showed positive 7B11 and K-2 staining; however, nearly all of the vacuolated lipoblasts showed strong 7B11 staining, only focal vacuolated lipoblasts in the adipocytic tumors were immunoreactive to K-2 positivity. All other components of the adipocytic tumors were non-reactive to 7B11, K-2, SP5, MIB-1, and SP6 in the cell membrane and cytoplasm. Our results showed that the 7B11 could well help to identify the lipoblasts, which would be useful to diagnose the malignant adipocytic tumors.