Residual Cancer Burden Index: Definition

The residual cancer burden (RCB) index measures the amount of cancer remaining in the breast and nearby lymph nodes after neoadjuvant therapy (treatment given before surgery). The index is used for the most common types of breast cancer, including invasive ductal carcinoma, invasive lobular carcinoma, invasive apocrine carcinoma, and invasive breast carcinoma (not otherwise specified).

The index combines several pathologic features into a single score and classifies the cancer’s response to treatment. The RCB was developed by doctors at the University of Texas MD Anderson Cancer Center (http://www.mdanderson.org/breastcancer_RCB).

Here’s how the score is calculated:

Pathologic features used in the RCB index

1. Size of the tumor bed in the breast: Pathologists measure the largest two dimensions of the tumor bed, which is the area where the tumor was located. This area may contain a mix of normal tissue, cancer cells, and scar tissue from the therapy.
2. Cancer cellularity: Cancer cellularity estimates the percentage of the tumor bed still containing cancer cells. This includes both invasive cancer (cancer that has spread into surrounding tissue) and in situ cancer (cancer cells that have not spread).
3. Percentage of in situ disease: Within the tumor bed, pathologists also estimate the percentage of cancer that is in situ, meaning that the cancer cells are confined to the milk ducts or lobules and have not spread into the surrounding tissue.
4. Lymph node involvement: The number of lymph nodes containing cancer cells (positive lymph nodes) is counted, and the size of the largest cluster of cancer cells in the lymph nodes is also measured.

These features are combined using a standardized formula to calculate the RCB score.

Patient groups

Based on the RCB score, patients are divided into four categories:

• RCB-0 (pathologic complete response): No residual invasive cancer is detected in the breast or lymph nodes.
• RCB-I (minimal burden): Very little residual cancer is present.
• RCB-II (moderate burden): A moderate amount of cancer remains.
• RCB-III (extensive burden): A large amount of cancer remains in the breast or lymph nodes.

Predicting disease-free survival

The RCB classification helps predict a patient’s likelihood of staying cancer-free after treatment. Patients with an RCB-0 classification typically have the best outcomes, with the highest chances of long-term survival without recurrence. As the RCB category increases from RCB-I to RCB-III, the risk of cancer recurrence increases, which may prompt additional treatments to reduce this risk.