Thymic Carcinoma in a Patient with Melanoma

Sir,

There have been several studies on second primary cancer with melanoma. A correct diagnosis of second primary malignancy in patients with melanoma is important for clinical management. Here, we present the first case of thymic carcinoma in a patient with melanoma.

An 81-year-old man was referred to our department for evaluation of a nodule on a dark-brown plaque on his right cheek. He noticed the plaque about 10 years ago and it had gradually enlarged. Three months before referral to our department, the nodule had developed within the plaque and showed rapid enlargement. He had no past and family history of malignancy. The plaque was 25 × 25 mm and the nodule was 14 × 14 mm in size [Figure 1a]. Cervical lymph nodes were not palpable. We suspected melanoma and performed excisional biopsy. Histopathological examination showed proliferation of atypical epithelioid and spindle melanocytes with minute melanin granules [Figure 1b and c]. The tumor thickness was 13 mm. Immunohistochemically, the tumor cells were positive for S-100 protein, Melan A, and HMB 45 [Figure 1d]. A diagnosis of melanoma was made. Positron emission tomography-computed tomography showed a nodule with high fluorodeoxyglucose uptake in the anterior mediastinum [Figure 1e]. Our differential diagnoses included metastatic melanoma of the thymus and second primary thymic carcinoma. We performed cutaneous lesion excision with a 2-cm margin and sentinel lymph node biopsy. In addition, robotic-assisted thymectomy was performed. The intraoperative pathological diagnosis of resected tumor was thymic cancer. Histopathological examination showed that the mediastinal nodule was squamous cell carcinoma [Figure 1f]. We made a final diagnosis of second primary thymic carcinoma in a patient with melanoma.

Figure 1.

(a) Physical examination revealed a nodule within a dark-brown plaque on the patient's right cheek. (b) Histopathological examination showed that atypical tumor cells had invaded into the subcutis (tumor thickness, 13 mm) (H and E staining, bar = 2 mm). (c) High-power magnification showed proliferation of epithelioid and spindle cells with melanin pigmentation (H and E staining, bar = 50 μm). (d) Tumor cells were positive for Melan A staining (bar = 250 μm). (e) PET-CT showed a nodule with high FDG uptake in the anterior mediastinum (yellow arrow). (f) A histopathological specimen of the mediastinal nodule showed proliferation of atypical squamous cells (H and E staining, bar = 50 μm)

There have been several studies on second primary cancer with melanoma.[1,2,3] Patients with cutaneous melanoma have been reported to have an increased relative risk for a second primary melanoma, breast cancer, prostate cancer, bladder cancer, and non-Hodgkin's lymphoma.[1,2,3] In patients with melanoma, the incidence rate of second primary cancer is 1.5%–20% of which second primary melanoma is the most common because of exposure to sun.[1,2] Therefore, we should be careful for secondary melanoma and as metastasis after treatment of primary melanoma. To our knowledge, however, there has been no report of thymic carcinoma in a patient with melanoma. Our patient had no past and family history of malignancy, and we considered that this case was accidental coincidence of melanoma and thymic carcinoma. A metastatic melanoma of the thymus diagnosed in patients with primary cutaneous melanoma has clinical importance because treatment for metastatic melanoma differs greatly from that for primary mediastinal cancer. Although it has not been known how frequent cutaneous melanoma metastasizes to the thymus, Einhorn et al. have reported that 11% of the patients with melanoma who had received autopsy had pericardium metastasis.[4] Therefore, mediastinal metastasis from cutaneous melanoma is more frequent than second primary thymic carcinoma in patient with cutaneous melanoma. Without a correct diagnosis, appropriate treatment cannot be performed. It is important to keep in mind the possibility of second primary cancer in patients with melanoma.

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Conflicts of interest

There are no conflicts of interest.