| As a unique population of tumor bulk, cancer stem cells have been implicated in tumor relapse
and chemoresistance in triple-negative breast cancer (TNBC). Therefore, understanding the
phenotype of cancer stem cells can pave the way for introducing novel molecular targeted
therapies for treating TNBC patients. Preclinical studies have identified CD44+CD24-/low as a
cancer stem cell phenotype; however, clinical studies have reported seemingly controversial
results regarding the prognostic values of CD44 and CD44+CD24-/low phenotype in TNBC
patients. To critically review the clinicopathological significance and prognostic values of CD44
and CD44+CD24-/low phenotype in TNBC patients, the Scopus, Embase, PubMed, and Web
of Science databases were systematically searched to obtain the relevant records published
before 20 October 2020. Based on nine included studies, CD44 and CD44+CD24-/low
phenotype are associated with inferior prognosis in TNBC patients. Moreover, these cancer
stem cell markers have been associated with advanced tumor stage, tumor size, higher tumor
grade, tumor metastasis, and lymphatic involvement in TNBC patients. Our evidence has also
indicated that, unlike the treatment-naïve TNBC patients, the tumoral cells of
chemoradiotherapy-treated TNBC patients can upregulate the CD44+CD24-/low phenotype
and establish an inverse association with androgen receptor (AR), leading to the inferior
prognosis of affected patients. In summary, CD44 and CD44+CD24-/low phenotype can be
utilized to determine TNBC patients’ prognosis in the pathology department as a routine
practice, and targeting these phenotypes can substantially improve the prognosis of
TNBC patients |