A positron emission tomography scan performed a few days after the discovery of metastatic prostatic adenocarcinoma in the SLNs showed expected postoperative changes (eg, increased activity from procedure-related inflammation) in the left side of the flank and axilla as well as moderately hypermetabolic left supraclavicular lymph nodes suspicious for viable metastatic disease. Subsequent fine-needle aspiration of the aforementioned lymph nodes revealed metastatic prostatic adenocarcinoma. The preoperative lymphoscintigraphy at the time of SLN biopsy did not show drainage to the left supraclavicular nodal basin.
Based on a discussion of the patient’s case during a multidisciplinary tumor board consultation, the benefit of performing completion lymph node dissection for melanoma management did not outweigh the risks. Accordingly, the patient received adjuvant radiation therapy to the axillary nodal basin. He was started on ketoconazole and zoledronic acid therapy for metastatic prostate adenocarcinoma and was alive with disease at 6-month follow-up. The finding of both metastatic melanoma and prostate adenocarcinoma detected in an SLN after wide excision and SLN biopsy for cutaneous melanoma is a unique report of collision of these 2 tumors. Rare cases of collision between 2 solid tumors occurring in the same lymph node have involved prostate adenocarcinoma as one of the solid tumor components.1,3 Detection of tumor collision on lymph node biopsy between prostatic adenocarcinoma and urothelial carcinoma has been documented in 2 separate cases.1 Three additional cases of concurrent prostatic adenocarcinoma and colorectal adenocarcinoma identified on lymph node biopsy have been reported.1,3 Although never proven statistically, it is likely that these concurrent diagnoses are due to the high incidences of prostate and colorectal adenocarcinomas in the general US population; they are ranked first and third, respectively, for cancer incidence in US males.4
As demonstrated in the current case and the available literature, immunohistochemical stains play a vital role in the detection of tumor collision phenomena as well as identification of histologic source of the metastases. Furthermore, thorough histopathologic examination of biopsy specimens in the context of a patient’s clinical history remains paramount in obtaining an accurate diagnosis. Earlier identification of second malignancies in SLNs can alert the clinician to the presence of relapse of a known concurrent malignancy before it is clinically apparent, enhancing the possibility of more effective treatment of earlier disease. As has been demonstrated for lymphoma and melanoma, in rare cases awareness of the possibility of a second malignancy in the SLN can result in earlier initial diagnosis of undiscovered malignancy.2