Brain metastases originating in breast cancer: clinical-pathological analysis and immunohistochemical profile

The incidence of brain metastases (BMs) originating in breast cancer (BC) is increasing due to advances in imaging techniques, which can detect such events early, and due to new therapies that can ensure longer survival. We performed a retrospective study on patients with BMs originating in BC and receiving surgical treatment in Neurosurgery Clinics of Prof. Dr. Nicolae Oblu Emergency Clinical Hospital, Iaşi, Romania, from January 2018 to December 2019. We identified 10 consecutive patients who underwent a craniotomy for a BMs originating in a BC (either for diagnostic purpose or with therapeutic intent). Clinicopathological data were collected from the electronic medical record and included the patient demographics (age at diagnosis of their BM), morphological characteristics of BM [location, cytopathological features, histopathological (HP) subtype, and immunohistochemical features, i.e., cytokeratin 5/6 (CK5/6), mammaglobin, estrogen receptor (ER), progesterone receptor (PR), and Ki67 labeling index (LI)], and time from BC diagnosis to BM diagnosis. Ninety percent of patients were in their sixth and seventh decades of life, with a median age of 57.9 years (47–65 years). Median time from BC diagnosis to BM was 34.42 months. Fifty percent of BMs were located in the parietal lobes, and 70% of all cases have multiple (≥2) BMs. All cases (100%) had a cytopathological examination, showing a hypercellular pattern, with poorly cohesive clusters of mild or pleomorphic cells, with nuclei with homogeneously distributed fine granular chromatin membrane, and with small or enlarged and irregular nucleoli. The dominant histopathology was invasive breast carcinoma of no special type (IBC-NST) (70%), but we also identified specific subtypes, i.e., tubular carcinoma (TC) (20%) and invasive micropapillary carcinoma (IMPC) (10%). Correlating location with HP subtypes of BMs from BC, IBC-NST and IMPC were located mostly in parietal lobes, and TC developed only in the occipital lobe. We found three patterns of immunostaining: (i) CK5/6 +/-, mammaglobin+, ER+, PR-, which was much more characteristic for IBC-NST; (ii) CK5/6-, mammaglobin+, ER-, PR-, being identified in tubular breast carcinoma; (iii) CK5/6 +/-, mammaglobin-, ER-, PR-, which were revealed by invasive micropapillary breast carcinoma. Our study revealed the fact that BMs originating in BC show heterogeneity of hormone receptor status, although morphologically there is not so much diversity. We also found a very variable Ki67 LI, which correlated especially with the morphological subtype.