Pathobiology of HER 2 positive small invasive (T1a,b) breast cancer: "A wolf in sheep's clothing".

Small invasive breast cancers (cancers with maximum diameter <1cm, T1a,b) become more prevalent form of breast cancer as a result of the introduction of breast cancer mammographic screening programs. Although associated with an excellent prognosis, T1a,b breast cancers are heterogeneous group of tumors with prognostically unfavorable subset of cases, primarily those with axillary lymph node metastases. To determine if the HER2 overexpression is associated with the prognostically unfavorable traditional clinicopathological features in this group of breast cancers, clinicopathological features (age, tumor size, histological type, histological grade, nodal status, hormone receptor status, proliferation index, lymphovascular invasion, ploidy) of 38 HER2 positive T1a,b cancers were compared with those of the control group consisting of 315 HER2 negative T1a,b cancers. The comparison of clinicopathological features was made using χ2 and t-test. HER2 positive T1a,b breast cancers were significantly associated with higher tumor grades (p<0.001), negative hormone receptors (p=0.008), presence of lymphovascular invasion (p=0.025), high proliferation index (p<0.001), and abnormal DNA content (p=0.04). We also noticed the higher frequency of lymph node positive cases in the HER2 positive group of cancers (p=0.05). There were no differences in age, tumor size and histological type between investigated groups. Our group of HER2 positive T1a,b breast cancers was associated with many unfavorable traditional prognostic factors, demonstrating that this subtype of early breast cancer has an aggressive biological phenotype which may have potential benefit from adjuvant chemo and immunotherapy.