Aim: Histopathologic diagnosis of a subset of uterine smooth muscle tumors is challenging. We report a critical review regarding the clinicopathological point of view of 62 cases of subsequently recurred or metastasized leiomyoma.

Methods: Medical records and glass slides of 62 cases of uterine smooth muscle tumor diagnosed as leiomyoma, which subsequently recurred or metastasized, were critically reviewed by pathologists specializing in gynecologic pathology and oncology. 

Results: In 47 (75.8%) of 62 cases, the diagnosis of leiomyoma was confirmed, including 11 intravascular leiomyomatosis (IVL) and benign metastasizing leiomyoma (BML). In 29 cases (46.8%) laparoscopic surgery was performed, of which morcellator without a bag was employed in 23 cases. Fifteen cases (24.2%) appeared to be underestimated and were re-classified as smooth muscle tumor of uncertain malignant potential (STUMP), leiomyosarcoma, or other malignant mesenchymal tumors. Recurrences in 7 cases (11.3%) were interpreted to be a malignant transformation, and one Smooth muscle tumor of uncertain malignant potential (STUMP) recurred as STUMP. 

Conclusion: The recurrence or metastasis in cases of “leiomyoma” is attributed to iatrogenic or under-evaluation of primary tumors, although a subset of cases is a rare example of biological progression.

This study was conducted with approval from the Institutional Review Board of Kurume University (number 15264). Assessed cases handled by 430 facilities registered with the Tumor Committee of the Japan Society of Obstetrics and Gynecology in which a uterine myoma diagnosed and treated between 2004 and 2013 subsequently showed clinical recurrence or metastasis. We performed a questionnaire for 430 facilities asking them to participate in the study. Of these facilities, 276 gave us answers to participate, and 30 out of 276 matched our study design. Regarding the definition of recurrence, although it is difficult to distinguish between recurrent and newly fibroids, according to the previously published article, recurrent myoma was defined as a myoma with a diameter of > 1cm. Pre-existent uterine and extrauterine myomas detected by MRI and/or ultrasonography excluded. All the primary myoma confirmed pathological diagnoses of leiomyomas and cases with suspicion of malignancy prior to surgery or with the postoperative diagnosis of malignancy were also excluded. A survey was conducted at the targeted facilities, and clinical information was collected from 62 cases handled by 30 facilities that agreed to participate in the survey. The contents of the survey included the following: patient age at the time of initial surgery, pregnancy and childbirth history, with or without magnetic resonance imaging (MRI) examinations, the procedure performed in the initial surgery, history of procedures using a morcellator (and bag), macroscopic findings at the time of the initial surgery, number of sectioned slides, pathological diagnosis, recurrence interval, the form of recurrence, details of the treatment administered at the time of recurrence, and patient status. Central pathology review was conducted using a multi-head microscope by four pathologists specializing in gynecological pathology (SS, HY, YM, and YO) and a consensus diagnosis was made. Of these, the primary lesions were also evaluated in 33 cases. The Stanford criteria established by Bell et al. were used to determine the malignancy of uterine smooth muscle tumors. According to the Stanford criteria, the presence of any two of the three following findings warrants a diagnosis of leiomyosarcoma: moderate to severe cytological atypia, coagulative tumor cell necrosis, and mitotic activity higher than 10 mf/10 HPFs. Subtypes of leiomyoma were classified according to WHO classification (4th edition).

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