The diagnosis of PCA is based on determining that a skin lesion has one of various shapes, presentations, and microscopic histological appearances. However, its diagnosis is considered difficult. PCAs have been misdiagnosed as various disorders including poromas, squamous cell carcinomas, basal cell carcinomas, seborrheic keratosis, nevi (i.e. moles), amelanotic melanomas, superficial spreading melanomas, pyogenic granulomas, fibromas, metastatic adenocarcinomas, verruca vulgaris (i.e. warts), Paget's disease of the breast-associated skin lesions, Merkel cell carcinoma, clear cell hidradenocarcinomas, and skin metastases from other cancers. PCA lesions have histological features which help distinguish them from these other skin lesions: they typically consist of medium-sized, rapidly proliferating cells with atypical nuclei, cell junctions, and intracellular formations of duct-like structures; may have areas of tissue that are necrotic and/or contain partially formed ducts lined with cuboidal/columnar epithelial cells (this last factor is a strong indicator of PCA); and often evidence invasion of nearby tissues. In unclear cases, the expression of key marker proteins by tumor tissue cells, as detected by immunohistochemistry analyses, has been used to clarify the diagnosis. For example, lesions containing tumor cells that express cytokeratins and CK 34B12 but not prostate specific antigen or prostatic specific acid phosphatase; p16 but not retinoblastoma protein; or carcinoembryonic antigen and NUC1 but negative for periodic acid–Schiff staining have been used to support the diagnosis of PCA. Detection of the YAP1-NUTM1 fusion gene transcripts or product protein in the tumor tissue cells of a lesion may also help identify a tumor as either a PCA or poroma. Finally, the presence of metastatic disease would indicate the lesion is not a benign lesion such as a poroma, seborrheic keratosis, nevus, fibroma, or wart.
Porocarcinoma
Poroma
Choriocarcinoma
Embryonal carcinoma
Embryoma
Polyembryoma
Seminoma
Leiomyosarcoma