Association of human breast cancer CD44(-)/CD24(-) cells with delayed distant metastasis

Tumor metastasis remains the main cause of breast cancer-related deaths, especially delayed breast cancer distant metastasis. The current study assessed the frequency of CD44(-)/CD24(-) breast cancer cells in 576 tissue specimens for associations with clinicopathological features and metastasis and investigated the underlying molecular mechanisms. The results indicated that higher frequency (≥19.5%) of CD44(-)/CD24(-) cells was associated with delayed postoperative breast cancer metastasis. Furthermore, CD44(-)/CD24(-)triple negative breast cancer (TNBC) cells spontaneously converted into CD44(+)/CD24(-)cancer stem cells (CSCs) with properties similar to CD44(+)/CD24(-)CSCs from primary human breast cancer cells and parental TNBC cells in terms of stemness marker expression, self-renewal, differentiation, tumorigenicity, and lung metastasis in vitro and in NOD/SCID mice. RNA sequencing identified several differentially expressed genes (DEGs) in newly converted CSCs and RHBDL2, one of the DEGs, expression was upregulated. More importantly, RHBDL2 silencing inhibited the YAP1/USP31/NF-κB signaling and attenuated spontaneous CD44(-)/CD24(-) cell conversion into CSCs and their mammosphere formation. These findings suggest that the frequency of CD44(-)/CD24(-) tumor cells and RHBDL2 may be valuable for prognosis of delayed breast cancer metastasis, particularly for TNBC.