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Discussion:The most likely diagnosis is metastatic melanoma (B). Though the patient had no obvious cutaneous lesions at the time of diagnosis and adamantly denied having any skin lesions, there are several indicators that melanoma is the correct diagnosis. The patient had a history of prolonged sun exposure (works as an automobile mechanic) and cytology with immunohistochemical staining showed S-100 and MART1 positivity, both markers of melanoma. Furthermore, melanoma often presents asymptomatically. Rarely, melanoma is associated with lesions that are painful or irritated [1]. The diagnosis of lymphoma (A) should be considered due to inguinal lymph node masses and presence of lung metastases. Lymphoma is however, unlikely given the lack of symptoms. Inguinal lymph nodes are non-tender and the patient did not endorse constitutional symptoms (fever, chills, night sweats, unintentional weight loss) [2].Colon cancer (C) is a plausible diagnosis given the patient’s age. The diagnosis is less likely though due to absence of associated symptoms (abdominal pain, symptomatic anemia, bowel changes and other signs of obstruction). Furthermore, metastatic colon cancer has a greater tendency to metastasize to the liver as opposed to the lymph node [3].The presence of lung mets and the bilateral nature of the inguinal masses go against a diagnosis of inguinal hernia (D). Furthermore, the patient does not have any signs concerning for incarceration such as pain. Lung cancer (E) is a reasonable diagnosis given the presence of masses in the lung. However, the masses in the lung are numerous and thus likely represent metastatic disease as opposed to primary lung cancer [4].Metastasis with unknown primary or MUP refers to the presence of malignant lesions without a known primary malignancy. This situation can represent melanoma. Approximately 90% of melanomas present with a cutaneous lesion. 2-3% of melanomas present within visceral organs or lymph node enlargement with an unknown primary site. There are two theories as to why this occurs. One theory is that the original cutaneous lesion regressed before presentation. Another theory is that melanocytes enter the lymph node and then transform into malignant cells that are then spread through lymphatics [5].Therapy for melanoma can be arranged into three groups: surgery, radiation and systemic therapy. The choice of therapy is based upon several factors including staging and affected sites. Surgery is usually an option for cancers consisting of one or fewer lesions. Distal metastasis often precludes surgical intervention. Surgery is also used as an adjunct to other types of therapy. In this case, surgery (C) is not the best treatment option because CT imaging revealed numerous pulmonary nodules likely representing metastasis [6].Radiation (A, E) is another option for treatment. It is rarely used to treat melanoma due to relative tumor radio-resistance. It is often used when there is CNS metastasis [6]. Systemic therapy consists of chemotherapy and immunotherapy. Immunotherapy is chemical therapy directed against specific parts of the cell cycle like check point inhibitors. Systemic therapy is often reserved for patients with metastatic disease (stage IV cancer). This patient has melanoma with suspected liver metastasis, therefore, systemic therapy is the best option. Chemotherapy (B) is a systemic treatment option but efficacy of treatment is not as significant as with immunotherapy. In this case, immunotherapy (D) is the best option for treatment [6]. Teaching points:Diagnose Melanoma based on positive immune staining. Incisional biopsy with immunohistochemical staining of the left inguinal lymph node revealed MART1 and S-100 positivity. Both stains are indicators of melanomaRecognize metastasis with unknown primary (or MUP). Patient was found to have melanoma but no cutaneous lesions were noted on exam. It is theorized that melanoma that presents as MUP is due to regression of cutaneous lesions prior to presentation or transformation of a melanocyte that has entered lymph node. References:R Pluta, A Burke, R Golub. Melanoma. JAMA. 2011 June; 305 (22):2368B Pace, C Lynn, R Glass. Lymphoma. JAMA. 2007 May; 297 (18):2044M Astin, T Griffin, R Neal, P Rose, W Hamilton. The Diagnostic Value of Symptoms for Colorectal Cancer in Primary Care: a Systematic Review. British Journal of General Practice. 201l; 61 (586): e231-e243. J Budczies, M von Winterfeld, F Klauschen. The Landscape of Metastatic Progression Patterns Across Major Human Cancers. Oncotarget. 2015 Jan; 6 (1): 570-583.J.N Cormier, Y Xing, L Feng. Metastatic Melanoma of lymph nodes in Patient with Unknown Primary Sites. Cancer. 2006 May 1; 106 (9): 2012-2020.S Bhatia, S.S Tykodi, J Thompson. Treatment of Metastatic Melanoma: An Overview. Oncology. 2009 May; 23 (6): 488-496.Brief Bio: Morolake Amole is a PGY-2 Internal Medicine resident at the University of South Florida. Her interests include Primary Care, Endocrinology and Health policy. She is specifically interested in complex medical diagnoses in the primary care setting and how health policy effects health outcomes. ................
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