MKI67 and leiomyosarcoma: Finally, the low growth fraction, revealed by the Ki67 labeling index in the present study, further indicates the benign nature of leiomyomas, thus discounting the diagnostic hypotheses of highly malignant neoplasms, including leiomyosarcomas, spindle-cell amelanotic melanomas and undifferentiated sarcomatoid carcinomas (14,15).