A 69－year－old man with a two-year history of having a pigmented lesion on his head developed a bleeding mass at the same site. After a skin biopsy was performed, he was diagnosed with malignant melanoma and subsequently referred to our hospital. Image examinations revealed brain and lung metastases. The primary and metastatic brain tumors were surgically resected. The BRAF mutation testing result was negative. Therefore, he was administered nivolumab monotherapy, which provided a partial response, as the lung metastases decreased in size. At the patient’s request, however, nivolumab was discontinued after 46 doses were administered. Two years passed since nivolumab discontinuation, with no increase in the lung metastases size or appearance of new metastases. This case highlights the lack of definitive guidelines on the optimal duration for treatment with immune checkpoint inhibitors. Here, we report on the duration of immune checkpoint inhibitor administration, with a review of relevant literature.[Skin Cancer (Japan) 2024 ; 39 : 145－151]

A 65－year－old female presented with a brown macule on her left lower thigh. Seven months before the initial consultation, a tumor appeared within the brown macule. A previous physician resected and diagnosed the patient with malignant melanoma. Computed tomography revealed lymphadenopathy of the left external and common iliac arteries. Since the tumor was negative for both BRAF－V600E/K mutations, nivolumab treatment was initiated. However, after the first administration, the patient developed fever with thyroid and liver dysfunction and refused further nivolumab treatment. A cancer gene panel test of the excised primary lesion revealed an NRAS mutation, suggesting that the MEK inhibitor was effective. Treatment with binimetinib was initiated using the nonstandard medical expense budget of our hospital. Twelve weeks after administration, some of the metastatic lymph nodes shrank. [Skin Cancer (Japan) 2024 ; 39 : 152－156]

A 46－year－old man with a 10－year history of hidradenitis suppurativa (HS) presented with a 5 cm wide, ulcerated, and granulomatous tumor in the perineum. Histopathology of the skin biopsy revealed squamous cell carcinoma (SCC). The patient underwent an en bloc resection of the perineal tumor and HS lesions, followed by skin flap reconstruction and split－skin grafting. The surgical margins were negative.

Three and a half years after the surgery was performed, the patient developed recurrent SCC in the perineum. The tumor was resected once more and the pelvic floor muscles were partially resected. The defect was reconstructed with split－skin grafting.

HS－associated SCCs are usually large and have a high recurrence rate. This case highlights the importance of long－term follow－up for patients with HS－associated SCC, even after surgical resection with negative margins.[Skin Cancer (Japan) 2024 ; 39 : 157－162]

A 52－year－old Japanese woman who underwent left mastectomy for breast cancer 13 years prior to presentation was referred to our department for evaluation of a rash on the left breast. Physical examination showed a central brown, depressed, firm, yellowish－white flat nodule (4×3 cm) at the site of the mastectomy scar, surrounded by firm yellowish－white nodules up to 1 cm in diameter. Dermoscopy revealed an atypical pigment network, blue－whitish veils, dots, globules, and arborizing vessels. Leaf－like structures and yellowish－white structureless areas were observed in the marginal region. Histopathological evaluation of a brown skin area revealed infiltration of breast tumor cells into the dermis and subcutaneous tissue with infiltration of large numbers of melanocytes and melanophages in the upper dermis. Dilated blood vessels and abundant fibrous stroma were observed in the dermis. Breast cancer that presents as a black－brown rash may show dermoscopic features of basal cell carcinoma and/or malignant melanoma.[Skin Cancer (Japan) 2024 ; 39 : 163－168]

A 72－year－old man observed a painless nodule on his left buttock 3 months before he visited a clinic. No significant changes occurred during this period. The nodule was surgically removed at the clinic ; however, histopathological findings indicated Merkel cell carcinoma, and he was referred to our department for further management. The patient presented with a pea－sized subcutaneous nodule on the left buttock, without any surface changes or palpable inguinal lymph nodes. The serum neuron－specific enolase level was normal at 8.7 ng/mL, and positron emission tomography－computed tomography showed no signs of metastasis. Histopathological evaluation showed a tumor in the dermis, with a pattern of irregular nest formation and fibrous stroma. The tumor cells were small and round, with scant cytoplasm, slightly varying nuclei, and rare mitotic figures. Immunohistochemistry revealed cells with CK20 immunopositivity in a dot－like pattern at the nuclear periphery together with immunopositivity for CAM5.2, synaptophysin, chromogranin A, and CD56. Sentinel lymph node biopsy of the left inguinal region did not reveal tumor cells. Postoperatively, the patient was administered radiotherapy (60 Gy) to the primary site and associated lymph nodes. No recurrence or metastasis was observed at the 4－year follow－up. Merkel cell carcinoma of the buttocks is rare. In this report, we summarize the characteristics of Merkel cell carcinoma of the buttocks.[Skin Cancer (Japan) 2024 ; 39 : 169－173]

A 70－year－old man developed a red nodule on the left upper arm two years before initial visit. Biopsy revealed Merkel cell carcinoma (MCC, positive for Merkel cell polyomavirus), which spontaneously regressed three weeks post－biopsy. Neither lymph node nor organ metastases were observed. Wide excision and sentinel lymph node biopsy revealed no residual tumor cells, and the disease was classified as T2N0M0 stage ⅡA (AJCC eighth edition). Despite the risk of immunosuppression because of oral PSL (10 mg), the patient declined adjuvant radiotherapy. After one year and seven months, he developed small intestine metastasis and peritoneal dissemination and died after two courses of avelumab. Although MCC often recurs and metastasizes, spontaneous regression has a favorable prognosis. In our case, MCC rapidly progressed after the initial spontaneous regression, emphasizing the need for careful post－regression monitoring, regardless of subsequent treatment.[Skin Cancer (Japan) 2024 ; 39 : 174－179]

A 74－year male presented with a small raised lesion in the right perianal area. The lesion was pea－sized, skin－colored, and raised with slightly soft elasticity and good mobility at first observation. A biopsy was performed under the suspicion of atheroma and dermatofibroma. Pathological examination　revealed basal cell carcinoma (BCC). At the initial examination, the lesion could not be suspected as malignant skin tumor clinically because of the tumor’s appearance and location. This rare case of BCC is thus presented here in addition to a review of BCC occurring on the perianal area.[Skin Cancer (Japan) 2024 ; 39 : 180－185]

A 75－year－old female from Shimane Prefecture presented with a month－long history of multiple pruritic erythematous lesions on the forearm. She reported no improvement with topical steroids and was referred to our department. Physical examination revealed annular erythematous plaques with an elevated peripheral rim on the trunk and extremities, and granuloma annulare was suspected. Histological findings from the erythematous plaques demonstrated Pautrier’s microabscesses in the epidermis and a nodular infiltrate of lymphocyte－like mononuclear cells and histiocytes in the dermis. The infiltrating atypical cells were CD3+, CD4+, CD7−, CD25+, and CCR+. In the central fading area of the erythema, histiocytes were observed around degenerated collagen fibers. Laboratory examination revealed leukocytosis (11.180/μL) with 11.3% of the abnormal lymphocytes. Serum assay results were positive for anti－HTLV－1 antibodies. The patient was diagnosed with adult T－cell leukemia－lymphoma. One month after the initial diagnosis, the number of abnormal lymphocytes increased rapidly ; however, the patient achieved a complete response after two cycles of CHOP therapy, four cycles of a combination of CHOP therapy and mogamulizumab, and four cycles of mogamulizumab alone.[Skin Cancer (Japan) 2024 ; 39 : 186－191]

Intravascular large B－cell lymphoma (IVLBCL) is a subtype of diffuse large B－cell lymphoma, in which tumor cells selectively proliferate within blood vessels, resulting in a variety of abnormalities. For a definitive diagnosis, the presence of tumor cells needs to be confirmed by histopathological examination. In this study, we investigated the usefulness of random skin biopsy, performed in our department, for the definitive diagnosis of 33 suspected IVLBCL cases. We focused on whether patients with negative skin biopsy results were ultimately diagnosed with diseases other than IVLBCL. Of the 33 cases, five were positive and definitively diagnosed with IVLBCL, and 27 were negative, except for one deceased patient. Additionally, all were ultimately diagnosed with diseases other than IVLBCL. These results suggest that this test is highly specific, with a positive result indicating a definitive diagnosis of IVLBCL and a negative result indicating absence of IVLBCL. To improve the usefulness of random skin biopsy, the accuracy of this test must be improved. As a key point for biopsy, priority should be given to skin eruptions, such as senile hemangiomas at three collection sites, if possible, and specimens should be taken at a depth sufficient to include fat.[Skin Cancer (Japan) 2024 ; 39 : 192－197]

A 65－year－old man presented with a mass in the pubic area that he first noticed approximately 40 years previously. On examination, we found a 97×54×25－mm pedunculated non－pigmented tumor. Basal cell carcinoma (BCC) was diagnosed by skin biopsy. Surgical excision with a 10－mm margin was performed, and the wound was closed in two stages. The tumor was a relatively rare polypoid BCC, and histopathological examination revealed micronodular BCC. In Japanese patients, BCC often appears on the face as a small pigmented tumor. However, it is difficult to diagnose if it occurs in the pubic area as a pedunculated non－pigmented tumor. Therefore, delayed diagnosis and inappropriate resection should be avoided.[Skin Cancer (Japan) 2024 ; 39 : 198－203]

Here, we present the case of multiple squamous cell carcinoma (SCC) and Bowen’s disease in a 32－year－old man who was diagnosed with FA at the age of 6. Over the past eight years, five skin tumors have been confirmed, with two occurring on the genital skin, one on the abdominal skin, and two on the occipital area. The tumors ranged from 4－18 mm in diameter and exhibited various appearances, including red lesions, black lesions, elevations, and ulcers. Each tumor was resected with a margin. Pathological examination showed three SCC and two Bowen’s disease. In Japan, while there have been 13 reports involving 17 cases of SCC in patients with FA, our case presents the first report of SCC occurring on the skin of this population, emphasizing its importance.[Skin Cancer (Japan) 2024 ; 39 : 204－213]