Background: Although the histopathologic differential diagnosis of pagetoid neoplasms is broad, unique histopathologic identifiers and clinical correlation can often identify the process. However, in the case of mammary Paget's disease (MPD) or extramammary Paget's disease (EPD) without an obvious underlying malignancy, distinction from pagetoid squamous cell carcinoma in situ (PSCCIS) can be challenging. Our goal was to better define the immunohistochemical staining patterns of these three entities in the hope of determining distinctive staining patterns.
Methods: We evaluated nine cases of PSCCIS, five cases of MPD, and 10 cases of EPD with the immunohistochemical antibodies CAM 5.2 and CK 5/6. In addition, only PSCCIS was stained with CK 7, as the staining patterns of CK 7 in MPD and EPD are well known from prior studies.
Results: CAM 5.2 diffusely stained all cases of MPD and EPD and failed to stain any case of PSCCIS. Furthermore, CK 7 only focally stained two of the 10 cases of PSCCIS. CK 5/6 was difficult to interpret due to the high functional background staining of the normal keratinocytes in the epidermis.
Conclusions: Based on these results, our data supports the use of CAM 5.2 and CK 7 immunoperoxidase markers in differentiating between difficult cases of PSCCIS and MPD or EPD. An antibody panel consisting of S-100, CAM 5.2, and CK 7 will aid in the accurate diagnosis of almost all pagetoid neoplasms of the breast or genital skin.