Clinical, histopathological and immunohistochemical features of brain metastases originating in colorectal cancer: a series of 27 consecutive cases.

Brain metastases (BMs) originating in colorectal cancer (CRC) have a significant importance for patients' survival. Because in literature there are only isolated case reports and only few series published on this issue, we aimed to assess the incidence of BMs from CRC, to identify patient's characteristics and BMs clinical, histopathological (HP) and immunohistochemical (IHC) features, and to compare the data we obtained with those from literature. We present a retrospective study of 27 histologically confirmed cases of BMs from CRC among all 1040 patients who received metastasectomy in the Department of Neurosurgery, Prof. Dr. Nicolae Oblu Emergency Clinical Hospital, Iaşi, Romania, in an eight-year period (January 2011 to December 2018). Patients' characteristics (gender, age), primary tumor location, time from primary tumor surgery to BMs surgery and BMs features (number, location and HP characteristics) were investigated. Histochemical [Alcian Blue (AB) and Periodic Acid-Schiff (PAS)] staining and IHC stainings for cytokeratin (CK) 7, CK20, caudal-type homeobox 2 (CDX2) and human epidermal growth factor receptor 2 (HER2)∕neu were performed on all available BMs specimens. There were 27 consecutive patients with BMs from CRC, corresponding to 2.59% of all patients with BMs during the eight-year period we have studied, most of them being diagnosed and treated in 2016. Male:female ratio was 1.45. The mean age for all patients at diagnosis of the BMs was 62.25 years (range: 40-79 years). The origin of the primary cancer was mainly the colon (62.96% of all cases). Of all 27 patients, only two (7.4%) presented neurological symptoms without a diagnosis of CRC. BMs were identified in a period ranging from six months to 70 months after the initial diagnosis. The average time between diagnosis of the primary tumor and of the BMs was 25.92 months. At the moment of the diagnosis of BMs, 17 (62.96%) patients also had other systemic metastases. Most of the cases (55.55%) were situated in the supratentorial compartment. IHC stainings were negative for CK7 and positive for CK20 and CDX2 in all BMs from colonic adenocarcinomas (ADCs), a profile consistent with a non-neuronal and gastric origin. AB and PAS stainings revealed pools of extracellular mucin, especially in cases of mucinous ADC. Ki67 labeling index ranged between 90% and 100%. IHC staining with anti-HER2∕neu antibody showed in 25 (96.15%) cases a strong and diffuse aberrant nuclear staining. BMs originating in CRC represent a rare pathology and have particular clinical and IHC features that could vary from one series to another series. In a few cases, BMs may be diagnosed in the absence of a known CRC diagnosis and in these situations, the correct diagnosis is of interest. However, a panel of antibodies can help in establishing a correct diagnosis. Our study was among the first to analyze the HER2∕neu expression pattern in BMs from CRC and we found a strong aberrant nuclear expression of this molecular marker on IHC investigation. Related to the data published so far in the literature, it is possible that HER2∕neu aberrant expression in the tumor nuclei of the BMs from our series may express the metastatic tumor cell phenotype that was previously subjected to cytostatics and radiation therapies. As such, we suggest that HER2∕neu aberrant expression in BMs originating in CRC could represent a proof for the worst prognosis of these patients.