Breast cancer with non-inflammatory skin involvement: Current data on an underreported entity and its problematic classification

We evaluated 166 breast cancer cases with non-inflammatory skin involvement (NISI), which were classified in the TNM classification as T4b. The distribution of tumour sizes and stages was: ≤3 cm:24.1%, 3.1–5 cm:21.7%, 5.1–10 cm:33.1%, >10 cm:21.1%; stages:I/II:21.0%, III:43.4%, IV:35.6%. To assess the impact of NISI on axillary lymph node involvement (ALNI), we analyzed a sub-group of 50 patients with tumours ≤5 cm and compared them with a matched control group. NISI was found to be associated with increased ALNI (HR, 2.66; 95%CI, 1.59–4.63; p < 0.0001). According to the inherent rules of tumour classification, only tumours with similar morphologic extent and prognostic significance should be combined. Since there is a high grade of heterogeneity, this basic tenet is clearly violated regarding breast cancer with NISI. Our proposal is to eliminate these tumours from the T4 category and to classify them simply by size (T1-3). Due to its prognostic significance, NISI should be indicated by an optional descriptor (e.g. S1).