Here is a very large leiomyoma of the uterus that has undergone degenerative change and is red (so-called "red degeneration"). Such an appearance might make you think that it could be malignant. Remember that malignant tumors do not generally arise from benign tumors, which is a good thing, because leiomyomas are so common (at least 20% of women will have one). Postmenopausally, leiomyomas tend to regress in size and become fibrotic.