Background: Basal-like breast carcinomas often are regarded for circumscribed solitary lesions having unfavorable prognosis. On the other hand, a considerable proportion of breast carcinomas is multifocal and has increased metastatic potential. In this study, we analyzed the subgross distribution of the lesions in a series of basal-like carcinomas, compared it with that in nonbasal-like tumors and studied the frequency of vascular invasion and lymph node metastasis in relation to focality of the lesions.
Methods: A total of 511 consecutive cases documented in large-format histologic sections were studied. Tumors expressing at least one of the basal (myoepithelial) markers (CK5/6, CK14, EGFR) in at least one of the invasive tumor foci were categorized as basal-like tumors. Triple-negative (ER/PR/HER-2-negative) basal-like carcinomas also were analyzed. The distribution of lesions and the frequency of vascular invasion and lymph node metastasis were analyzed. The study was approved by the Regional Ethical Committee Uppsala-Örebro.
Results: In 44% of cases, the invasive component was multifocal or diffuse. Combining the in situ and invasive tumor components resulted in 61% of cases with multifocal/diffuse distribution. The only statistically significant difference observed was that basal-like tumors lacked in situ components more often (21% vs. 9%; P = 0.0075). No significant differences could be demonstrated regarding vascular invasion and lymph node status. Lymph node metastasis appeared significantly more frequently in multifocal cases in both tumor categories.
Conclusions: Basal-like breast carcinomas are as frequently multifocal as their non-basal-like counterparts; multifocality is associated with increased risk for vascular invasion and lymph node metastasis in both tumor categories.