[Preliminary study on proliferative characteristics of the mixed tumor]

DNA-content was quantitatively determined in 2 monomorphic adenomas, 16 mixed tumors and 3 malignant mixed tumors by image analysis technique. While 7 cases of mixed tumor show slow proliferative activity similar to that of monomorphic adenomas, there are 6 cases of mixed tumor in which active proliferation and the appearance of polyploid and aneuploid (AN) below 10% are found. In 3 cases of mixed tumor the proportion of AN is above 10%, indicating abnormal proliferation as that of malignant mixed tumor. The results indicate that mixed tumors need to be considered as being composed of various kinds of biological behavior. Mixed tumors with long preoperation duration (> or = 6 years) are characterized by an increase in the number of proliferation diploid and AN as compared to that with short (< or = 3 years) preoperation duration (P < 0.01). Mixed tumors with the size > 2.5 cm have more AN than that with the size < or = 2.5 cm (P < 0.01). The results indicate that the risk of malignant transformation of a benign mixed tumor increases as it grows.