HIF1A and breast cancer: Alterations in other claudins further underscore their diverse roles: elevated CLDN4 expression is associated with lymph node metastasis and enhanced cancer cell stemness, while loss of CLDN6 can increase breast cancer cell motility and resistance to apoptosis, facilitating invasion [13,14,15,16].Another study suggested that CLDN6 is transcriptionally upregulated by HIF-1α under hypoxic conditions [17].