Tumor to Tumor Metastasis from Adenocarcinoma Not Otherwise Specified of the Parotid Gland to Uterine Leiomyoma: Presentation of a Unique Case

Salivary gland adenocarcinoma not otherwise specified (NOS) is a malignant epithelial tumor composed of ductal/glandular structures with or without cystic formation. Histologically it is classified as high grade with relevant biological behavior. Although both minor and major glands may be involved, the majority (60%) implicate the parotid gland. Location, regional lymph node status, and histological grade are some of the factors that predict the progress of the disease and the development of metastases. Long follow-up is considered the standard option as distant metastases (DM) may occur despite regional control. Primary sites of DM, besides lymph nodes, include bone, lung, and liver. Herein we report a unique case of a 68-year-old female with a previous history of high-grade adenocarcinoma NOS of her right parotid gland. On her biannual follow-up examination, MRI revealed an abnormal increase in the size of a known uterine leiomyoma of the posterior uterine wall. Positron emission tomography-CT (PET-CT) showed increased uptake in the uterus and lungs. On frozen section, adenocarcinoma was found at the center of the leiomyoma. Histological and immunohistochemical findings were consistent with secondary involvement by the salivary gland adenocarcinoma NOS. Treatment consisted of cyclophosphamide, adriamycin, and cisplatin with poor outcome. The patient was lost to follow-up. Review of the literature indicates that no similar case has been reported in the English literature.