3. Discussion
Herein, we report a case in which radiation therapy using the Quad Shot regimen was effective in the treatment of cutaneous metastasis from parotid gland cancer. The most common sources of cutaneous metastases have been reported to be breast cancer, colorectal cancer, and melanoma in women and melanoma, lung cancer, and colorectal cancer in men.1 Cutaneous metastasis from salivary gland cancer similar to this case is uncommon.6-8
The optimal treatment of cutaneous metastases has not yet been established. Wong et al . recommended surgical excision of metastasis, which would result in a significant decrease in total tumor burden, improve quality of life, or result in increased functionality.1 They also indicated that therapy in patients with widespread unresectable cutaneous and subcutaneous metastases is limited to other types of palliative therapy such as radiation therapy, systemic chemotherapy, cryotherapy, laser ablation, or radiofrequency ablation.
Radiation therapy is an effective treatment method for cutaneous metastasis. However, its optimal dose and fractionations remain unclear. Arase et al . reported a case of cutaneous metastasis to the chest wall from prostate adenocarcinoma. In the case, durable tumor shrinkage and symptom relief was achieved after radiation therapy using 18 Gy in 3 fractions using electron.9 Oike et al . reported a case of cutaneous metastasis of non-small cell lung cancer to the arm. In that case, photon radiation therapy at 45 Gy in 15 fractions led to complete tumor remission and improved the patient’s quality of life.3
The Quad Shot regimen, which consisted of 2 days of twice-daily fractionation with a fraction size of 3.5–3.7 Gy (14.0–14.8 Gy per cycle) repeated at 3–6-week intervals for a total of three cycles, was originally devised for advanced pelvic malignancies (RTOG 8502).10 Recently, the Quad Shot regimen has been successfully adapted for palliative treatment of head and neck cancer.4,5 The Quad Shot regimen for head and neck cancer has been reported to achieve a tumor response rates of 53–77% and palliation rates of over 80% with minimal toxicity.11 Some reports showed the efficacy of the Quad Shot regimen for primary skin cancer.12,13However, to the best of our knowledge, there is no report of using the Quad Shot regimen in patients with cutaneous metastasis.
In this case, cutaneous metastasis was widespread and surgical resection was difficult. Radiation therapy was administered using the Quad Shot regimen for extensive cutaneous metastasis of the chest wall. The treatment resulted in significant tumor shrinkage and relief of symptoms including exudate and pain. Only grade 1 dermatitis was observed as a radiation-induced adverse event; no severe adverse events were observed. Thus, the Quad Shot regimen may be a safe and effective treatment option for cutaneous metastases.
Some studies have shown that palliative radiation therapy using the Quad Shot regimen in combination with chemotherapy was effective in symptom relief and well-tolerated.14,15 In this case, radiation therapy using the Quad Shot regimen was performed concomitant with chemotherapy consisting of 5-fluorouracil, cisplatin, and pembrolizumab. The treatment resulted in favorable symptom relief effect was and could be safely completed with no serious adverse events.
In conclusion, the Quad Shot regimen may be a safe and effective treatment option for cutaneous metastases.