Extensive cutaneous metastasis from salivary gland adenocarcinoma: A rare occurrence

Dear Editor,

Cutaneous metastases occur in less than 10% of patients with malignancies. Among the primary tumours that may result in skin metastasis, breast cancer, lung cancer, and melanoma are the most common.¹ Salivary gland neoplasms are extremely rare, and about 70% of these tumours are benign.² Adenocarcinoma, a subtype of high-grade salivary gland malignancy, is even rarer. There is minimal likelihood of cutaneous metastases from salivary gland malignancy, as evidenced by a single centre study with only 3 cases (n=64).³ Cutaneous metastases often present a formidable clinical diagnostic challenge. They often present as rapidly enlarging, painless subcutaneous nodules, with varied morphologies including macules, infiltrated or indurated plaques, bullous or papulosquamous lesions.⁴ While cutaneous metastases are typically localised, close to the primary tumour, cases of distant metastasis present additional diagnostic hurdles. Herein, we report a case of cutaneous metastasis arising from salivary gland adenocarcinoma, characterised by extensive proliferation of lesions involving the unilateral chest and shoulder region.

An 82-year-old man underwent surgery for left salivary gland tumours in 2021. Histopathologic examination revealed poorly differentiated adenocarcinoma infiltrating both the left submandibular and parotid glands with concomitant metastasis to the left hyoid and cervical lymph nodes. He received radiotherapy for one-month post-surgery.. Two years later, the patient presented with localised erythema involving left breast. Initial treatment with topical antiviral and antibiotic ointments resulted in minimal improvement. The lesions followed a progressive course, extending from the left breast and shoulder region toward the midline, accompanied by pruritus and discomfort. Physical examination revealed extensive papules, plaques, and nodules. Many were centrally ulcerated with exudation and haemorrhage [Figure 1]. Smaller ulcerated papules appeared to be umbilicated. The underlying skin was indurated.

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Figure 1:

Lesions spread from the left chest and shoulder region to the midline, characterised by extensive ulcerated papules, plaques, and nodules.

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Histopathologic examination revealed a poorly differentiated adenocarcinoma infiltrating the dermis [Figure 2a-b]. These aberrant, pleomorphic cells exhibited sporadic mitotic activity and were positive for CAM 5.2, AE1/AE3, cytokeratin-5/6 (CK-5/6), CK-7, and carcinoembryonic antigen by immunohistochemical analysis [Figure 2c-d]. Conversely, Delta N p63 and Napsin A were negative in these tumour cells. These findings were consistent with cutaneous metastases arising from the salivary gland adenocarcinoma. Additionally, a CT scan revealed metastases in the bilateral axillary lymph nodes and lungs, with no apparent liver or bone involvement [Figure 3]. Palliative therapy was initiated, and the patient was referred to oncology for a thorough evaluation and development of treatment strategies.

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Figure 2a:

Metastatic poorly differentiated salivary gland adenocarcinoma infiltrating the dermis. A diffuse cellular infiltrate infiltrating into the dermis without obvious epidermal involvement (Haematoxylin & eosin, 100x).

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Figure 2b:

Pleomorphic cells with scattered mitotic activity (Haematoxylin & eosin, 200x).

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Figure 2c:

CK-7 immunohistochemical study highlighted the tumour cells (100x).

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Figure 2d:

Cytokeratin Antibody Monoclonal (CAM) 5.2 immunohistochemical study highlighted the tumour cells (100x).

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Figure 3:

Computed tomography scan image. High-density nodular shadows were seen in the lungs, indicating possible metastatic cancer.

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The present patient presented with extensive papules, plaques, and nodules, a relatively uncommon presentation. He initially presented with localised erythema resembling radiation dermatitis. In addition, the unilateral distribution and associated discomfort mimicked herpes zoster. A definitive diagnosis required pathologic evaluation. At the same time, the anaplastic nature of metastases made it difficult to determine their tissue origin.⁴ The patient had been diagnosed with adenocarcinoma of the left salivary gland two years prior to the onset of the lesions. At that time, unilateral lymph node metastasis was noted, without other abnormalities. Histopathology of the skin lesions also revealed poorly differentiated adenocarcinoma, with supportive immunohistochemical data confirming the diagnosis. Taken together, these findings indicated that the skin lesions were cutaneous metastases arising from salivary gland adenocarcinoma. The presence of lung and lymphatic metastases in this patient suggests potential haematologic and lymphatic pathways for the dissemination of tumour cells. .

Metastases from salivary gland malignancies predominantly affect the bones, lungs, liver, and lymph nodes.² However, diagnosis of metastases at these sites often requires costly and invasive procedures, causing diagnostic delay. . In contrast, skin examination offers a convenient and non-invasive means of monitoring. Meanwhile, skin invasion is associated with an increased risk of poorer outcomes.³ Therefore, oncologists should stress the importance of being vigilant for skin abnormalities during follow-up. Patients should be educated to report nodules, slow-healing ulcers or other rapidly progressing skin lesions. Early detection of cutaneous metastases facilitates prompt identification of cancer recurrence and metastasis, allowing clinicians to intervene early and potentially improve patient survival.

The optimal management of cutaneous metastases remains unclear. Localised lesions can be treated by surgical excision, whereas patients with extensive unresectable cutaneous metastases are often limited to palliative therapies such as radiotherapy, systemic chemotherapy, isolated limb perfusion, IFN-α injections, cryotherapy, or laser ablation.⁴ Okada et al. documented a similar case of extensive cutaneous metastases arising from parotid gland cancer that was successfully palliated by the “quad shot” regimen of radiotherapy and concurrent chemotherapy with 5-fluorouracil, cisplatin, and pembrolizumab.⁵ This strategy may represent a viable and effective treatment modality for cutaneous metastases. However, investigations for more systematic and comprehensive treatment modalities are warranted.