American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following is a key indicator of high risk for recurrence in patients treated for colorectal cancer?

1. Well-differentiated histology

2. Absence of vascular invasions

3. Positive resection margins

4. Negative lymphatic involvement

The correct answer is: Positive resection margins

The identification of positive resection margins as an indicator of high risk for recurrence in patients treated for colorectal cancer is significant for several reasons. When surgical resection of a tumor is performed, the goal is to remove not just the tumor itself but also some surrounding tissue to ensure that all cancerous cells are eliminated. Positive resection margins indicate that cancer cells are present at the edge of the resected tissue, which suggests that not all cancerous tissues have been completely removed. This is concerning because any residual cancer cells could lead to recurrence of the disease after treatment. In contrast, well-differentiated histology typically suggests a slower-growing tumor with a potentially better prognosis, rather than an increased risk of recurrence. The absence of vascular invasion is considered a favorable feature because it implies that the cancer has not spread through the bloodstream, which also reduces the likelihood of recurrence. Similarly, negative lymphatic involvement, where the cancer has not spread to nearby lymph nodes, is a positive prognostic factor, indicating a lower risk of metastasis and recurrence. Given that positive resection margins directly correlate with the likelihood of leftover cancerous cells and therefore an increased risk of recurrence, this option stands out as a crucial indicator in assessing a patient's prognosis after colorectal cancer treatment