Atypical and malignant granular cell tumors in Japan: a Japanese Musculoskeletal Oncology Group (JMOG) study.

BACKGROUND

Malignant granular cell tumors (MGCTs) are extremely rare neoplasms with only a limited number of studies published to date. The aim of this study is to elucidate the clinicopathological characteristics and prognostic factors of MGCTs.

METHODS

This is a multi-institutional retrospective study of MGCTs with a central pathological review. A total of 18 cases were retrieved. Specimens were blindly reviewed by two pathologists based on the diagnostic criteria by Fanburg-Smith et al. Kaplan-Meier survival probabilities were calculated, and risk factors for poor prognosis were evaluated.

RESULTS

Three and fifteen cases were diagnosed as atypical GCTs (AGCTs) and mGCTs according to the Fanburg-Smith et al. classification, respectively. Four (one atypical and three malignant) cases had metastasis at the first presentation, including lymph node metastasis. Three out of ten cases treated with wide resection developed local recurrence. Although prolonged static disease periods of ≥1 year were observed in four cases receiving chemotherapy, all cases with local recurrence or metastasis, including two atypical cases, eventually died of disease. The 5- and 10-year overall survival rates for localized MGCTs were 69.2 and 34.6 %, respectively. The presence of necrosis was revealed as a risk factor associated with adverse clinical outcomes.

CONCLUSIONS

MGCTs have high rates of recurrence and metastasis including lymph node metastasis. As histologically atypical cases also have metastatic potential, close attention should be paid to AGCTs. The combination of histological evaluation and tumor size may lead to more accurate diagnosis of this rare neoplasm.