Table 3.

Summary of MiRNAs associated with Tamoxifen resistance in breast cancer

miRNA	Role	Expression in BC	Molecular Mechanism	Outcome	Ref
miR-519a	OncomiR	UP	Targets PTEN, RB1, CDKN1A; activates PI3K/cell cycle	↑Proliferation, ↑Tamoxifen resistance, Poor survival	[100]
miR-221/222	OncomiR	UP	Targets p27Kip1, ERα; exosomal transfer; HER2 + tumors	↑Proliferation, ↓Apoptosis, ↑Tamoxifen resistance, Biomarker	[12, 101, 102]
miR-155	OncomiR	UP	Targets SOCS6, activates STAT3	↑Survival, ↑Tamoxifen resistance, ↓Apoptosis	[103]
miR-9-5p	OncomiR	UP (exosomal)	Represses ADIPOQ	↓Apoptosis, ↑Tamoxifen resistance	[104]
miR-92a-3p	OncomiR	UP	Regulates IL-6/STAT3, Wnt/β-catenin, complex networks	↑Tamoxifen resistance, Poor prognosis	[105]
miR-27b-3p	Tumor Suppressor	DOWN	Targets NR5A2, CREB1	↑Tamoxifen sensitivity, ↓Proliferation, ↓Aromatase	[106]
miR-342	Tumor Suppressor	DOWN	Regulates apoptosis, cell cycle (targets TXNIP, EVL)	↑Apoptosis, ↓Growth, ↑Tamoxifen sensitivity, ↑Survival	[107, 108]
miR-320a	Tumor Suppressor	DOWN	Targets ARPP-19, ERRγ, c-Myc/Cyclin D1 axis	↓Proliferation, ↓Colony formation, ↑Tamoxifen sensitivity	[109]
miR-449a	Tumor Suppressor	DOWN	Targets ADAM22 (affects PPARG, KRAS, LYN)	↑Tamoxifen sensitivity, ↓Tamoxifen resistance	[110]
let-7b/let-7i	Tumor Suppressor	DOWN	Targets ER-α36, inhibits MAPK/Akt pathways	↑Tamoxifen sensitivity, ↓MAPK/Akt, ↓ER-α36	[111]
miR-375	Tumor Suppressor	DOWN	Targets MTDH, reverses EMT	↑Tamoxifen sensitivity, ↓EMT, ↓Invasion	[112]
miR-873	Tumor Suppressor	DOWN	Targets CDK3, inhibits ERα phosphorylation	↓Proliferation, ↑Tamoxifen sensitivity	[113]