Dual Immunohistochemical Detection of Mitoses in Melanoma

Excerpt

Mitotic rate in melanoma is the second most powerful independent predictor of survival outcome after tumor thickness [1]. The mitotic rate plays a critical role in the 2008 American Joint Committee on Cancer (AJC) TMN staging on melanoma [2]. Mitosis can be obscured by mitotic mimickers such as apoptosis, karyorrhectic debris, and mitosis in non-melanocytic cells make the definitive determination of mitotic rate difficult. The immunohistochemical stain phosphohistone H3 is expressed nearly exclusively by cells during the metaphase component of the cell cycle [3, 4]. The metaphase component of the cell cycle is characterized chromosomal condensation and coiling. The metaphase component of the cell cycle is recognizable in H&E stained tissue through identification of mitotic figures. The antigen expression during this exclusive period of cell division creates an ideal nuclear target for immunohistochemical detection of mitotic figures. PHH3 is expressed in nearly all cells during metaphase so an additional marker is necessary to properly identify the mitotically active cells of interest. Melanoma-associated antigen recognized by T cells (MART-1) provides another useful target as this antigen’s target is expressed in the cytoplasm of melanocytes [5]. Combining the sensitivity and specificity of PHH3 for mitotic figures and the sensitivity of MART-1 for melanosomes, cells that are dual stained with both antigens can reliably be quantified as mitotic figures in melanocytes. This dual stain approach allows the user to ignore the cells only staining with PHH3 during the mitotic count as they represent mitotically active cells that are not melanocytes. …