2. Case presentation
A 72-year-old man presented to our hospital with a left parotid mass and cutaneous tumor on the chest wall. The parotid tumor was pathologically diagnosed as an adenocarcinoma. Additionally, the cutaneous tumor was considered a metastasis from the parotid gland carcinoma. The tumor tissues were positive for androgen receptors and human epidermal growth factor receptor 2 (HER2). Cutaneous metastases spread from the midline precordium to the left chest and shoulder, accompanied by exudate and bleeding (Figure 1A). The patient also had edema of the left upper extremity. Computed tomography showed cutaneous, multiple lymph node (neck, subclavian, and axilla), and intramuscular metastases (Figure 2A). Upper extremity edema was considered to be due to axillary/subclavian lymph node metastasis.
Chemotherapy consisting of 5-fluorouracil, cisplatin, and pembrolizumab administered every 4 weeks (5-fluorouracil:1000 mg/m2, day 1-4; cisplatin:100 mg/m2, day 1; pembrolizumab:200 mg, day 1) was selected as the initial treatment. Simultaneously, radiation therapy using the Quad Shot regimen (2 days of twice-daily fractionation with a fraction size of 3.5 Gy) was performed for the cutaneous and axillary/subclavian lymph node metastases with a combination of electrons and X-rays (Figure 3). Similar radiation therapy was repeated three cycles at 3-week intervals (Figure 4).
Four weeks after the first Quad Shot, the exudate and bleeding significantly decreased. As the treatment progressed, the cutaneous metastases shrank and flattened (Figure 1B, C, D). Computed tomography showed tumor shrinkage. However, intramuscular metastases outside the irradiation increased, and a left pleural effusion appeared (Figure 2B). Grade 1 dermatitis (according to the Common Terminology Criteria for Adverse Events, version 5) was identified as an acute adverse event of radiation therapy. Grade 3 leukopenia and grade 1 thrombocytopenia were determined as chemotherapy-related adverse events. After the second course of chemotherapy, the patient developed grade 2 pituitary dysfunction, which was considered an immune-related adverse event caused by pembrolizumab.
Chemotherapy with 5-fluorouracil, cisplatin, and pembrolizumab was continued for five courses, but the disease progressed. As second-line chemotherapy, docetaxel (80 mg every 3 weeks) was started. From the fourth course, trastuzumab (400 mg every 3 weeks) was added to docetaxel because HER2 positivity in the tumor was confirmed by dual-color in situ hybridization. After changing the chemotherapy regimen, a reduction in tumor lesions was observed. Seven months after treatment initiation, the irradiated cutaneous metastases remained free of regrowth.