Breast cancer involves the uncontrolled growth of cells, typically starting in the milk ducts or lobules. While most diagnoses involve a single, identifiable tumor (unifocal disease), some cases present with multiple distinct cancerous growths within the same breast. This presentation, known as multifocal breast cancer, complicates standard disease classification and treatment planning. Accurately determining the stage of multifocal disease relies on specific guidelines to assess the overall extent of the cancer.
Differentiating Multifocal and Multicentric Disease
The terms multifocal and multicentric are often used interchangeably, but pathologically, they are distinct based on tumor location. Multifocal disease involves two or more invasive tumor foci located within the same quadrant of the breast. These tumors are often thought to have spread along the same ductal system, suggesting they arose from a single original cancer cell clone.
In contrast, multicentric disease involves two or more tumors located in different quadrants, separated by a significant distance or normal tissue. This suggests the tumors arose from separate, independent cell transformations. While the distinction is important for surgical planning, the rules for assigning a stage are the same for both presentations, focusing only on the characteristics of the largest tumor identified in the breast.
Determining the Tumor (T) Category
The Tumor (T) category, which reflects the size of the primary tumor, is determined using the American Joint Committee on Cancer (AJCC) staging system. For multifocal or multicentric disease, a specific rule applies: the T category is determined solely by the measurement of the largest invasive tumor focus. The size of any smaller, secondary tumor foci is ignored when assigning the T size classification.
For example, if a patient has three invasive tumors measuring 2.5 cm, 1.0 cm, and 0.5 cm, the cancer is staged based on the largest dimension (2.5 cm). This size places the cancer in the T2 category, which encompasses tumors larger than 2 cm but not greater than 5 cm. This approach is used because the largest mass is generally considered the most biologically aggressive component of the disease.
Although the size of smaller tumors does not influence the T category, the presence of multifocality is recorded in the pathological report. This detail can affect the overall prognostic stage, which integrates the anatomical T, N, and M categories with biological factors like tumor grade and receptor status. Standard anatomical staging relies on the largest single focus, even though some research suggests the aggregate tumor size may be a more accurate predictor of outcomes.
Evaluating Nodal and Metastatic Status (N and M)
The overall stage of breast cancer is completed by assessing the Nodal (N) and Metastasis (M) status, which describe the extent of cancer spread beyond the primary site. The N category is determined by the presence and extent of cancer cells found in the nearby lymph nodes, particularly those in the axilla. The number of tumor foci in the breast does not change the criteria used to define the N category.
The presence of multiple tumors is consistently associated with an increased likelihood of cancer spreading to the lymph nodes. Patients with multifocal disease may have a significantly higher risk of nodal involvement compared to those with similar-sized unifocal tumors. This elevated risk makes multifocality a serious consideration, even if the T category is based only on the largest tumor size. The M category, which addresses distant metastasis, is handled identically to unifocal disease, classifying cancer as either absent (M0) or present (M1) in distant organs.
Combining the T, N, and M categories provides the anatomical stage group, typically expressed as Roman numerals (I to IV). This final overall stage guides treatment decisions. Because of the higher probability of nodal involvement, a thorough evaluation of the N status is necessary to accurately determine the overall stage and prognosis for multifocal disease.
Impact on Surgical Treatment Options
The presence of multifocal disease significantly influences the choice of local surgical treatment, regardless of the determined T stage. For a single unifocal tumor, breast-conserving surgery (lumpectomy) followed by radiation is often an option. However, when multiple tumor foci are scattered across a quadrant or the entire breast, achieving clear surgical margins becomes a complex challenge.
Historically, multifocal and multicentric breast cancer often resulted in a recommendation for mastectomy (surgical removal of the entire breast). This ensured the elimination of all known tumor foci. Current data, often aided by advanced imaging like magnetic resonance imaging (MRI), suggests that breast-conserving therapy may be safe for select patients with multiple lesions. This is true if the tumors are small and close enough to be removed with a single excision that allows for an acceptable cosmetic outcome. If a lumpectomy is performed for multifocal disease, radiation therapy is universally required afterward, often with a radiation boost to each tumor bed.