Myoma Hot Spot: Tumor-to-Tumor Metastasis of Thyroid Origin into Uterine Leiomyoma

Introduction: Distant metastases of papillary thyroid cancers are rare. Most common metastatic sites include bone and lung, whereas metastases to brain, eye, breast, liver, kidney, muscle, and skin are infrequent and almost always appear in advanced-stage tumor disease. Metastases to ovary and/or uterus are even scarcer. We report herein a very exceptional case of asymptomatic malignant-to-benign tumor-to-tumor metastasis of thyroid origin into a uterine leiomyoma. Case Presentation: We present the case of a 53-year-old female patient who had a previous history of pT1b N0 M0 R0 papillary carcinoma of the lower left thyroid lobe, treated by total thyroidectomy and central lymph node dissection and two successive administrations of radioactive treatment with iodine-131. Six years later, follow-up imaging disclosed an asymptomatic slow-growing 40-mm-long pedicled subserous heterogeneous uterine myoma including a 12-mm hypervascular nodule, which was suspicious for thyroid malignancy on MRI. Discussion: Histopathology of a hysterectomy specimen disclosed a hypervascular well-limited poorly differentiated trabecular carcinomatous infiltration within the uterine leiomyoma. The immunohistochemical profile of the suspicious nodule was compatible with a thyroid origin. Conclusion: A hypervascular "hot spot" intramyoma nodule was the diagnostic clue in a clinical context of hematogenous tumor spread of thyroid origin (increased thyroglobulin level).