Most common extra-intestinal malignancy in HNPCC:
**Core Concept**
Hereditary Non-Polyposis Colorectal Cancer (HNPCC) is a genetic disorder characterized by an increased risk of developing colorectal cancer and other extra-intestinal malignancies. The genetic alterations in HNPCC lead to microsatellite instability, which is a hallmark of this condition.
**Why the Correct Answer is Right**
The most common extra-intestinal malignancy in HNPCC is endometrial cancer, accounting for approximately 40-50% of extra-intestinal cancers in HNPCC patients. This is due to the microsatellite instability caused by mutations in DNA mismatch repair genes, such as MLH1 and MSH2, which are also responsible for colorectal cancer development in HNPCC. Endometrial cancer in HNPCC often presents as early-onset, endometrioid adenocarcinoma.
**Why Each Wrong Option is Incorrect**
**Option A:** Ovarian cancer is not the most common extra-intestinal malignancy in HNPCC, although it is a known association. However, the risk is significantly lower compared to endometrial cancer.
**Option B:** Uterine sarcomas are rare and not typically associated with HNPCC.
**Option C:** Renal cell carcinoma is not a common extra-intestinal malignancy in HNPCC.
**Clinical Pearl / High-Yield Fact**
Early-onset endometrial cancer in women with HNPCC should prompt genetic testing for MLH1 and MSH2 mutations, as well as consideration of prophylactic hysterectomy and bilateral salpingo-oophorectomy.
**Correct Answer: D. Endometrial cancer.**