Ectopic thyroid tissue is a rare condition manifested as the appearance of thyroid tissue outside the thyroid gland. Here, we report a case of ectopic thyroid tissue in the breast. A 48-year-old Chinese woman who was diagnosed with breast cancer received modified radical mastectomy. A thyroid tissue was found on subsequent pathological examination. The ectopic thyroid tissue was confirmed by immunohistochemistry staining of thyroid biomarkers, including thyroglobulin, thyroid transcription factor-1, and thyroid peroxidase. Currently, abnormal thyroid anlage descent is the main theory to explain ectopic thyroid tissue, especially lingual thyroid. However, it is far-fetched to explain the pathogenesis of ectopic thyroid tissues existed in organs or tissues far from thyroid such as iris, cardiac, pulmonary, duodenal, adrenal, and vertebral. Here, we reviewed the previous cases of ectopic thyroid tissue in breast and proposed a “entoderm migration” theory to explain distant ectopic thyroid tissues based on embryonic development perspective.

Pulmonary benign metastasizing leiomyoma (PBML) is a type of benign metastasizing leiomyoma (BML), which metastasizes to lungs. In view of the rarity and nonspecific imaging characteristics of PBML, this condition is easily misdiagnosed as malignant lung cancer. This is a case report of a 39-year-old lady in whom multiple bilateral lung nodules were found during a health checkup and was diagnosed with PBML. The patient had recurrent uterine fibroids and underwent myomectomy twice, 7 years and 3 years ago, respectively, before the diagnosis of PBML was made. This patient was asymptomatic, and regular examinations were normal. Her laboratory investigations were all within normal range. Computed tomography (CT) showed multiple nodules in bilateral lungs. In order to confirm the disease, thoracoscopic nodule resection and tissue biopsy were performed. Hematoxylin eosin (HE) staining showed spindle-shaped cells, while immunohistochemical staining revealed positive for desmin, smooth muscle actin (SMA), estrogen receptor (ER), and progesterone receptor (PR), which are all PBML markers. The patient was followed-up without any further treatment. After 8 months of follow-up, CT scan revealed an increased number of nodules. This is unique case because of the recurrence of uterine fibroids, which means that the patient is susceptible to it. Our report may give a new insight to the relationship between the susceptibility of uterine fibroids and the onset and progression of PBML.