Myxoid leiomyosarcoma of the uterus.

AIMS: Recent guidelines have suggested the presence of tumour cell necrosis (TCN), atypia and mitotic index as major features in the distinction of myxoid leiomyosarcomas (MLMSs) from myxoid leiomyomas. The aim of this study was to focus on an invasive growth pattern as a significant feature in this distinction in the absence of TCN.

METHODS AND RESULTS: Twelve uterine smooth muscle tumours with myxoid change in ≥60% of the lesion were interpreted as MLMS on the basis of the presence of focal mild atypia as well as one or more of the following features: (i) infiltrative growth pattern; (ii) vascular invasion; (iii) mitotic index of ≥5 mitotic figures (m.f.)/50 high-power fields (HPFs); and (iv) a combination of at least focal severe atypia and at least 2-4 m.f./50 HPFs. Unequivocal TCN was not evident in any of these tumours. The various morphological features were correlated with outcome. With follow-ups ranging from 19 to 113 months (mean 60 months), five of the 12 women developed recurrences, and two of them died. Nine of the 12 tumours had an infiltrative growth pattern, and all five recurrent tumours were from this group.

CONCLUSION: In the absence of TCN, an infiltrative margin is a major factor related to the potential for aggressive behaviour of MLMS.