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BACKGROUND Multiple synchronous, ipsilateral, invasive foci of breast carcinomas are frequent and are associated with a poorer prognosis. Few studies have investigated the prognostic and therapeutic implications of heterogeneity of such foci. METHODS The authors reviewed the tumor type, grade, and size of all invasive foci in a series of 110 multifocal breast carcinomas documented on large‐format slides. Molecular phenotype was determined by immunohistochemistry in tissue microarray blocks using 3 classification systems. The survival of patients who had tumors with microscopic (tumor type and/or grade) heterogeneity and of those who had tumors with phenotypic heterogeneity was compared with the survival of patients who had multifocal homogeneous tumors using Kaplan‐Meier curves. The hazard ratio of dying from breast cancer was also calculated. RESULTS Intertumoral heterogeneity in tumor type and grade was detected in 16 of 110 tumors (14.6%) and in 6 of 110 tumors (5.5%), respectively. The molecular phenotype of invasive tumor foci within the same breast differed in 10% to 12.7% of patients (11‐14 of 110 tumors), depending on the classification system used. Patients who had phenotypically heterogeneous, multifocal cancers had a greater risk of dying from disease (HR=2.879; 95%CI=1.084−7.649; P = .034) and had significantly shorter survival (P = .016). Phenotypic differences were most common in patients who had tumors that were homogeneous in terms of tumor type (11 of 18 tumors) and histology grade (14 of 18 tumors). Phenotyping additional tumor foci had the potential to influence the therapeutic decisions in up to 8 patients. CONCLUSIONS Phenotyping more than 1 invasive focus of multifocal breast carcinomas only if the individual foci deviate microscopically appears to be insufficient, because phenotypic intertumoral heterogeneity may be observed in microscopically identical foci and has potential prognostic and therapeutic consequences. Cancer 2014;120:26–34. © 2013 American Cancer Society.

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We analyzed 301 consecutive cases of 1-14-mm invasive breast carcinomas documented in large-format histological sections to determine the distribution of invasive and in situ foci. We also aimed to determine whether this distribution was related to the frequency of demonstrable vascular invasion and lymph node metastases. One third of the carcinomas (31.9%, 96 cases) had a multifocal invasive component and a more than doubled relative risk of vascular invasion (RR = 2.3642, 95% confidence interval (CI) = 1.5077-3.7073) and lymph node metastasis (RR = 2.7760, 95% CI = 1.6337-4.7171) compared to unifocal invasive carcinomas. Invasive carcinomas with diffuse in situ component had an elevated relative risk for vascular invasion (RR = 2.2201, 95% CI = 1.4049-3.5083) and lymph node metastasis (RR = 1.9201, 95% CI = 1.1278-3.2691) compared to those with unifocal or multifocal in situ lesions. However, multifocality of the invasive component was associated with a substantially elevated risk of vascular invasion and lymph node metastasis, even in cases with diffuse in situ component. Similar observations were made in the 1-9- and 10-14-mm invasive carcinoma subgroups. These findings indicate that lesion distribution has prognostic relevance for 1-14-mm invasive breast carcinomas and underline the importance of using special techniques in breast pathology for proper assessment of this parameter.

BACKGROUND:The prognostic significance of molecular phenotype in breast cancer is well established in the literature. Recent studies have demonstrated that subgross lesion distribution (unifocal, multifocal, and diffuse) and disease extent also carry prognostic significance in this disease. However, the correlation of molecular phenotypes with subgross parameters has not yet been investigated in detail. METHODS: In total, 444 consecutive invasive breast cancers that were documented in large-format histology slides and worked up with detailed radiologic-pathologic correlation were sampled into tissue microarray blocks and stained immunohistochemically to delineate the molecular subtypes. RESULTS: Diffuse or multifocal distribution of the invasive component of breast carcinomas in this series was associated with a 4.14-fold respectively 2.75-fold risk of cancer-related death compared with unifocal tumors irrespective of molecular phenotype. Patients who had human epidermal growth factor receptor 2 (HER2)-positive cancers; estrogen receptor-negative, progesterone receptor-negative, and HER2-negative (triple-negative) cancers; or basal-like cancers had a 2.18-fold, 2.33-fold, and 4.07-fold risk of dying of disease, respectively, compared with patients who had luminal A carcinomas. Unifocal luminal A, HER2-positive, and basal-like cancers were associated with significantly better long-term survival outcomes than their multifocal or diffuse counterparts; luminal B and triple-negative tumors also had the same tendency. In multivariate analysis, patient age, tumor size category, lymph node status, lesion distribution, and molecular phenotypes remained significant. CONCLUSIONS: Multifocality and diffuse distribution of the invasive component were associated with significantly poorer survival in women with breast carcinomas compared with unifocal disease in patients with luminal A, HER2 type, and basal-like cancers. Molecular classification of breast cancer is a powerful tool but gains in power when combined with conventional and subgross morphologic parameters. Cancer 2013;119:1132-9. V C 2012 American Cancer Society.KEYWORDS: breast, breast cancer, multifocality, diffuse, molecular phenotypes, survival. INTRODUCTIONBreast cancer mortality has decreased significantly in countries that have organized, population-based mammography screening 1 ; however, despite using the most recent diagnostic tools and modern therapeutic regimens, women are still dying from this disease. Therefore, exploring the prognostic information generated by radiologic, histologic, and molecular tumor characteristics is essential to facilitate individualized treatment and further decrease disease-specific mortality.Patient age, tumor size, histologic grade, and lymph node status still remain powerful prognostic indicators in patients with breast cancer.2,3 On the other hand, many second-generation prognostic parameters have emerged and have been introduced into routine practice, and the most prominent are estrogen receptor (ER), progesterone recepto...