Angiomyolipoma arising in the gluteal region:

Perivascular epithelioid cell tumors (PEComas) of the bone and soft tissue: a Japanese Musculoskeletal Oncology Group (JMOG) multi-institutional study

PURPOSE

Perivascular epithelioid cell tumors (PEComas) of the bone and soft tissues are rare mesenchymal neoplasms, some of which are malignant. However, their clinical and pathological characteristics remain unclear. This study was performed to investigate the clinical and pathological characteristics of PEComas in bone and soft tissues by leveraging information from the Japanese Musculoskeletal Oncology Group.

METHODS

Nine patients, including four male and five female patients with a median age of 50 years, were retrospectively reviewed. PEComas of the visceral organs, including the uterus and retroperitoneum, were excluded.

RESULTS

Eight tumors arose in the soft tissue and one in the bone, with a mean size of 8.8 cm. Four patients showed local recurrence or distant metastasis. The 1-year survival rate was 78%. Pathologically, eight tumors were classified as malignant and one as having uncertain malignancy potential. Half of the tumors showed high MIB-1 index values of > 30%. Immunohistochemically, the melanocyte marker HMB45 was expressed in 89% of the cases, and muscle-specific markers were expressed only in 30-50% of the cases. Transcription factor binding to IGHM enhancer 3 (TFE3) expression was positive in 100% of the patients. Tumors with high expression of TFE3 were classified as PEComas with malignant potential according to Folpe's classification.

CONCLUSIONS

Bone and soft tissue PEComas may have a higher malignancy potential than other visceral PEComas and are more likely to develop as TFE3-rearranged PEComas.

Unusual multicentric angiomyolipoma of knee joint and soft tissue foot

To report unusual occurrence of angiomyolipoma at intraarticular location with another lesion in the same side foot. A 12-year-old girl was referred to us after initial inconclusive work-up done elsewhere for swelling of left knee joint. There was a 15 × 12 cm swelling in the knee joint partially encasing patella while also a similar hourglass shaped swelling measuring 9 × 4 cm was noted in the same side foot. After clinical and radiological evaluation an excision biopsy was planned for both sites. The specimen sent for histopathological evaluation revealed angiomyolipoma with identical characteristics in the two locations and was HMB45 immunostain negative. Patient was evaluated for possibility of tuberous sclerosis but there was no contributory evidence. Angiomyolipoma is typically a solitary renal tumor with rare occurrence at musculoskeletal sites. Multicentric variety is still infrequent. Intraarticular occurrence of angiomyolipoma presents a diagnostic challenge not only in terms of unfamiliarity but also unusual presentation with absence of characteristic immunostaining and multicentricity requiring careful exclusion of other lesions that may require a more radical approach for treatment.