Clinical Impact of Breast Cancer Stem Cells in Metastatic Breast Cancer Patients

Breast tumors are composed of phenotypically diverse groups of cells; however, it is unclear which of these cells contribute to tumor development. Breast cancer management usually targets proliferating cells, but as breast cancer stem cells are slowly cycling, they may escape these targets whenever they are not actively proliferating. This may explain the occurrence of recurrences and failure of the treatment.

To assess the impact of the BCSC expression on progression-free survival (PFS), overall survival (OS), and tumor response in metastatic breast cancer patients and to correlate the BCSC expression with different clinicopathological parameters.

This prospective study enrolled 76 de novo metastatic breast cancer patients recruited from the Oncology Center, Mansoura University, Egypt, with a minimum age 31 years and a maximum of 70 years. Pretreatment BCSC markers (CD44 and CD24) were assessed by immunohistochemistry on formalin-fixed paraffin-embedded tumor tissues from a primary or metastatic site. Patients received different lines of treatment, hormonal or chemotherapy, according to their biological subtypes. Anti-Her2 was added for Her2-positive patients.

Thirty-three patients (43.4%) were premenopausal and 43 patients (56.6%) were postmenopausal. Bone-only metastasis was seen in 12 patients (15.7%), however, visceral ± bone metastasis was seen in 64 patients (84.3%). BCSC markers (CD44+ve and CD24-ve) were expressed in 32 patients (42.1%), while 44 patients (57.9%) were not expressing BCSC markers. Out of 32 patients expressing BCSC, 22 patients (68%) were premenopausal and 28 patients (87.5%) were with high-grade (GIII) disease. BCSC was significantly presented in triple negative subtype breast cancer as there were 32 patients with the BCSC expression, and out of them, 15 patients (46.9%) had triple negative disease, 10 patients (31.3%) had luminal subtype, and seven patients (21.9%) were Her2-amplified, while there were 44 patients without BCSC expression, and out of them, 30 patients (68.2%) were of the luminal subtype, no patient (20.5%) had triple negative disease, and five patients (11.4%) were Her2-amplified (P 0.006). Twenty-four patients (31.5%) presented with visceral crisis; out of them, 17 patients (70.1%) were expressing BCSC which also denoted more aggressive disease. Seventy-four patients were candidates for the response assessment. BCSC-expressing patients showed poor response compared to non-BCSC (16.1% responsive versus 51.2%, respectively), with a significance relation (P 0.003). The BCSC expression was associated with both significant short PFS (median, 18 months vs. 35 months; P=0.001) and short OS (median, 26 months vs. 43 months; P=0.003). In multivariate analysis; BCSC expression was an independent prognostic factor for poor OS (P=0.055) along with the molecular subtype (P=0.012), Her2 status (P=0.011), and histologic grade (P=0.037).

This study further validates the BCSC expression as a poor prognostic biomarker correlated with poor response, short PFS and OS. So, it could be used as a marker for tailoring treatment with different lines of therapies in further studies. The BCSC expression was highly presented in the triple negative subtype which is an aggressive disease that lacks different targets. So, targeting BCSC may carry a hope in future for this group of patients.