Correlation of Tumor Volume and Surface Area with Lymph Node Status in Patients with Multifocal/Multicentric Breast Carcinoma

BACKGROUND. Multicentric breast carcinomas have a higher frequency of axillary lymph node metastasis than unifocal tumors of similar stage. It remains unclear whether this merely reflects larger tumor volumes or a different biologic behavior. The authors have shown previously that when aggregate tumor diameter are used for staging, unifocal and multifocal tumors have a similar frequency of axillary lymph node metastasis. However, summing diameter overestimates actual tumor volume because volume is proportional to the third power of the diameter. Therefore, the aim of the current study was to reanalyze the relation between size and axillary lymph node status by correcting for tumor volumes and surface areas. METHODS. Volumes and surface areas of 122 breast tumor specimens with multiple macroscopic nodules (two foci: n = 95; three foci: n = 22; three foci: n = 5) were calculated by approximating the shape of each tumor nodule to an ellipsoid (for volume) or to a prolate spheroid (for area). For comparison, the authors used an internal control series, comprised of 469 macroscopic unifocal tumors. For all patients, multiple assessments of largest tumor size and combined size of all foci were correlated with the status of axillary lymph nodes. The associations between lymph node status, tumor volume or area, and multifocality were modeled using univariate and multivariate logistic regression. RESULTS. When either the largest or the aggregate tumor volume was used as a size estimate, tumor specimens with multiple nodules had a higher frequency of lymph node involvement compared with unifocal tumors of a similar volume or area. The odds ratio (OR) for having positive lymph nodes was 2.34 for aggregate volume measurement (P < 0.001). Surface area estimates yielded similar results (OR = 2.2, P < 0.001). CONCLUSIONS. Breast tumors with multiple macroscopic nodules had a different biology, with a propensity to dissemination at smaller tumor volumes (i.e., there was another factor besides volume alone that accounted for the differences in behavior).