Porocarcinoma

[2] This cancer typically develops in individuals as a single cutaneous tumor in the intraepidermal spiral part (termed the acrosyringium) of these sweat glands' ducts (i.e. channels) at or near to where they open on the skin's surface.

[5] Porocarcinomas are malignant counterparts to the far more common benign tumors of the eccrine sweat gland's acrosyringium, i.e. poromas.

[12] Because of their rarity and lack of distinct clinical features and variable physical and microscopic histological appearances, the diagnosis of porocarcinomas is often challenging.

[4][9] Under-diagnosis may have been responsible for a recent study conducted in a United Kingdom single center that reported that the number of PCA cases had increased 3-fold over the previous 4 years and was expected to rapidly rise further during the next decade.

Metastasis (most commonly involving the lymph nodes close to the primary lesion) were diagnosed at presentation in 31% of cases.

[2] Other studies report that: a) PCA tumors presented with average sizes of 2.53 cm (range of 0.3–7 cm) in largest diameter;[11] b) PCA tumors at presentation were commonly red to violet in color, usually <2 cm in maximum diameter; and typically asymptomatic but may have been called to attention because of spontaneous bleeding, ulceration, sudden itching, pain, or rapid growth;[13] c) in 37 cases, metastases were present in 16.2% of cases at presentation and occurred in two cases (5.4% of cases) 3 and 17 months after diagnosis;[4] d) no metastatic disease was found at presentation or after a 3-year follow-up in 7 cases;[10] e) PCA have metastasized to nearby or distal skin sites, local lymph nodes, or to the bones, bladder, breast, retroperitoneum, ovary, liver, lung,[11] brain, or stomach;[2] and f) PCA have been reported to occur in skin areas previously traumatized or exposed to radiation, excessive sunlight, or chronic lymphedema; in a sebaceous cyst; and in individuals with extramammary Paget's disease, sarcoidosis, chronic lymphocytic leukemia, pernicious anemia, Hodgkin's disease, nevus sebaceous, HIV/AIDS, xeroderma pigmentosum, immunosuppression caused by a disease or chemotherapy, pernicious anemia, and xeroderma pigmentosa.

Cancers associated with the overexpression or overactivation of the TEAD transcription factors include those of the breasts, kidneys, stomach, liver, colon, rectum, prostate, brain (i.e. medulloblastomas), and the head and neck area (i.e. squamous cell carcinomas).

Further studies are needed to determine if the latter fusion or mutated genes can be used as diagnostic markers or therapeutic targets for treating PCA tumors.

[4] 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.

[20] Metastases are more likely to be present with PCA lesions that: a) develop spontaneous bleeding, ulceration, sudden itching, pain, or rapid growth;[4][13] b) are accompanied by enlarged sentinel lymph nodes, i.e. lymph nodes draining the tumor site;[10] c) consist of poorly differentiated cells as detected on biopsy;[11] d) penetrate 7 mm or more into the skin; e) contain rapidly proliferating cells as defined by the presence of 14 or more cells undergoing mitoses per high power microscopic field;[9] or f) occur in the perineum, trunk, or lower limb.

[17] In these cases, studies recommend that patients be more fully examined for metastases before surgery using lymphadenectomy (i.e. lymph node dissection) in order to check for metastasis in, and remove, lymph nodes draining the site of the skin tumor[10] and by magnetic resonance, positron emission tomography–computed tomography, X-ray,[17] ultrasound imaging methods[10] to detect metastases.

[16] Patients that failed to have their disease completely removed with surgical/radiation/lymphadenectomy procedures or have surgically inaccessible metastases are usually treated with various drug regimens.

[16][20] The two patients treated with pembrolizumab obtained a complete and excellent responses that continued at follow-up examinations done respectively 24 and 18 months after treatment.