**Core Concept**
Leiomyoma, also known as uterine fibroids, are benign tumors arising from the smooth muscle layer of the uterus. These tumors can cause a variety of symptoms due to their growth and location, and can be influenced by hormonal changes during the menstrual cycle.

**Why the Correct Answer is Right**
Leiomyomas are typically characterized by an increase in cell number and size, leading to an enlargement of the uterus. However, they are usually not malignant and do not invade surrounding tissues. The most common symptoms of leiomyomas include abnormal uterine bleeding, pelvic pressure or pain, and urinary frequency. The growth of leiomyomas can be influenced by estrogen, which is why they often shrink after menopause.

**Why Each Wrong Option is Incorrect**
**Option A:** Red degeneration is a known complication of leiomyomas, particularly during pregnancy. It occurs when the tumor outgrows its blood supply, leading to ischemia and hemorrhage. This is not the least likely complication.

**Option B:** Leiomyomas can cause a variety of hormonal changes, including an increase in estrogen production. This can lead to an increase in the size of the tumor, as well as other symptoms such as endometrial hyperplasia. This is not the least likely complication.

**Option C:** Leiomyosarcoma is a rare type of cancer that can arise from leiomyomas. This is the least likely complication of leiomyomas, as they are typically benign.

**Option D:** Infection is a possible complication of leiomyomas, particularly if the tumor becomes necrotic or if there is a breach in the uterine wall. This is not the least likely complication.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that leiomyomas are usually benign, but they can cause significant symptoms and complications. The risk of leiomyosarcoma is low, but it's essential to consider this diagnosis in cases of rapidly growing tumors or those with atypical features.

**Correct Answer: C. Leiomyosarcoma is a rare type of cancer that can arise from leiomyomas.**