After staging evaluation for invasive ductal carcinoma, which procedure is required to detect microscopic nodal spread?

• A. Axillary lymph node dissection
• B. Bone marrow biopsy
• C. Sentinel lymph node biopsy
• D. Pelvic MRI

Answer: (D)

Detecting microscopic nodal spread in invasive ductal carcinoma relies on identifying the first lymph node that drains the tumor, because metastasis often follows this pathway. This is accomplished with a sentinel lymph node biopsy, which maps and removes the sentinel node to check for cancer cells. If the sentinel node is free of cancer, other axillary nodes are unlikely to be involved, allowing the patient to avoid a more extensive surgery. If cancer is found in the sentinel node, more extensive axillary lymph node dissection or directed therapy may be considered, but the initial, less invasive test provides the crucial staging information with less morbidity.

Axillary lymph node dissection is more invasive and used when metastasis is already suspected or confirmed, not as the initial test for micrometastasis. Bone marrow biopsy isn’t routine for nodal spread in breast cancer and pelvic MRI isn’t relevant for assessing axillary nodal involvement.