BML is a disease in which a tissue from a benign uterine leiomyoma is detected as a solitary nodule or as multiple nodules in the lungs of patients with a previous history of hysterectomy for uterine leiomyoma. In 1939, Steiner et al
] were the first to report BML as metastasizing fibroleiomyoma of the uterus, and since then there have been several similar reports.
Abramson et al
] reported that the average age of patients with BML is 48 years old, that the period from hysterectomy to nodule discovery is variable from three months to 26 years and that the first symptom of BML may sometimes be cough or chest pain although it can also be almost indiscernible. Horstmann et al
] reported that the radiological presentation of BML can be as multiple nodules in 87% of cases (bilateral nodules, 70% and unilateral nodule, 17%) or as a solitary nodule in 13% of cases. The main metastatic site of BML is the lung but other sites, including lymph nodes, soft tissue of the pelvis, bone, bone marrow, greater omentum, peritoneum and heart, have been also reported [4
]. Tsunoda et al
] reported only one case of benign metastasizing leiomyoma of the lung complicated with primary lung cancer. To the best of our knowledge, there are no cases in the literature about the association between lung cancer and BML other than this report. Thus, we believe that this is a very rare case of BML associated with primary lung cancer.
Recent studies have shown that BML is caused by lung metastasis of uterine leiomyoma, which is histologically a benign tumor with a very low grade of malignancy; uterine leiomyoma has been reported to depend on sex hormones [1
]. On the other hand, Patton et al
] have previously reported that BML results from the monoclonal, hematogenous spread of an apparently benign uterine leiomyoma. However, these conclusions are still controversial.
Pathological examination of the BML in our case showed spindle-shaped cells without mitotic activity or nuclear atypia, surrounded by cuboidal bronchiolar epithelial cells; additional immunohistochemical staining showed that the spindle-shaped cells derived from smooth muscle cells of the uterus, and that the low cuboidal metaplastic cells derived from pre-existing bronchial cells [4
]. The presence of TTF-1 is usually assessed to confirm the diagnosis of primary non-small cell lung carcinoma (especially adenocarcinoma) [10
]; the purpose of TTF-1 staining in our particular case was to decide whether the low cuboidal metaplastic bronchiolar epithelium observed in the pathological specimens derived from the pre-existing bronchiolar epithelium, because it is known that TTF-1 is only expressed on the normal epithelium of the lung and thyroid [10
]. We believe that the diagnosis of BML is not dependent on the expression of TTF-1. Pathological comparison between the solitary pulmonary nodule and the original uterine tumor should provide confirmatory evidence but the sample was not available. However, the small lung nodule was diagnosed as BML based on the results of the immunohistochemical staining and the past history of hysterectomy for uterine leiomyoma.
There is no standard therapy for BML. Recently, Patton et al
] suggested the possibility of hormonal treatment for BML with positive immunoreactivity for ER and PgR. Other studies have shown improvement of BML after ovariectomy, administration of progesterone or gonadotropin-releasing hormone agonist and menopause [11
]. The prognosis of the disease is also unclear. In the present reported case, although the pathological stage of lung carcinoma was stage IA, we considered that CT follow-up was necessary at intervals of three to six months including follow-up of BML recurrence. No additional therapy was done and the follow-up by chest CT showed no recurrence of the BML or lung cancer.