of poorly differentiated cells as detected on biopsy; 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; or f) occur in the perineum, trunk, or lower limb. 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 and by magnetic resonance, positron emission tomography–computed tomography, x-ray, ultrasound imaging methods to detect metastases. pca cases in which surgical resection of the primary tumor does not remove all malignant cells or the tumor recurs at its site of removal (~20% recur at the primary site within a year of excision) have been treated with repeated resections and/or local radiation therapy. adjuvant radiation therapy may also be useful to treat localized apc tumors that are at high-risk of metastasizing such as tumors that are >5 cm in maximal diameter, have invaded lymphatic vessels, or contain poorly differentiated cells. 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. these regimens have included 5-fluorouracil (i.e. 5-fu) alone, 5-fu & cisplatin, 5-fu & adriamycin & paclitaxel, docetaxel & carboplatin, paclitaxel & carboplatin & intralesional (i.e. injected directly into the lesion) interleukin 2, topical diphenylcyclopropenone (a drug which is primarily used to treat warts), intralesional interleukin 2 alone, interferon alfa & isotretinoin, topical 5-fu, intra-arterial (i.e. injection of a drug into a small artery that supplies blood to a tumor) docetaxel, or the immunotherapy drug, pembrolizumab. 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. in general, however, there has been no highly and repeatedly successful drug treatments specified for metastatic pca: the cited drug treatment regimens have been used in too few cases to be properly evaluated and in general produced no, minimal, or only very short-term benefits. prognosis although most studies have observed patients for short periods and do not mention survival times, survival rates, or definitive prognoses, some studies have reported that localize pca may be successfully treated by surgical removal. however, pca has often been reported to be a very aggressive malignancy that is a) that is found to be metastatic at diagnosis in approximately 20% to 30% of patients; b) recurs after surgical removal in another ~20% of cases; and c) carries a poor prognosis with survival times that are often just a few months after diagnosis regardless of management. however, a recent study of eight pca cases found no nodal positivity, recurrence, or death after follow-ups. further studies are need to define the prognosis of pca.