What question did this study set out to answer?

To examine the rare behavior of metastasizing pleomorphic adenoma, which retains benign histology while showing malignant metastasis.

July 6, 2026Open Access

The paradox of benign histology and malignant behavior: lymphatic metastasis in pleomorphic adenoma—a case report

MNMelika NematolahzadeKerman University of Medical Sciences HEHadi EslamiRafsanjan University of Medical Sciences TMTouraj Reza MirshekariKerman University of Medical Sciences

Key Points

To examine the rare behavior of metastasizing pleomorphic adenoma, which retains benign histology while showing malignant metastasis.
Reported a case of a 31-year-old female with a history of pleomorphic adenoma.
Used ultrasonography to identify a multinodular mass and lymphadenopathy in the cervical region.
Conducted surgical excision and histopathological examination to confirm diagnosis.
Lymph node involvement was confirmed in the patient, despite the tumor's benign histological features.
The patient had a 12-year latency period from initial tumor excision to metastasis.
The case emphasizes the necessity for long-term surveillance of pleomorphic adenoma patients.

Abstract

BACKGROUND: Metastasizing pleomorphic adenoma is an exceptionally rare variant of salivary gland neoplasms that maintains histologically benign features while demonstrating metastatic behavior. Lymph node involvement is particularly uncommon, representing only 20.1% of reported metastatic cases. CASE PRESENTATION: A 31-year-old Iranian female patient presented with a progressively enlarging left cervical mass developing over 4 years. Her history included surgical excision of a pleomorphic adenoma 12 years prior. Ultrasonography revealed a complex multinodular mass within the submandibular salivary gland and distinct lymphadenopathy in the left lateral neck. Surgical excision and histopathological examination confirmed metastasizing pleomorphic adenoma with lymph node involvement, maintaining characteristic benign cytological features despite its metastatic presentation. CONCLUSION: This case of metastasizing pleomorphic adenoma, occurring after a 12-year latency period, clinically supports the contemporary hypothesis that a long incubation time of residual disease, rather than recurrence itself, is a critical factor for metastatic transformation. The report contributes to the limited literature on the lymphatic dissemination of this tumor and powerfully underscores that indefinite long-term surveillance is mandatory for all patients with a history of pleomorphic adenoma. Finally, it highlights the diagnostic paradox that persists when advanced molecular testing is unavailable, reinforcing that clinical vigilance is paramount regardless of a benign histological report.

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