Background: Silibinin (SB), the main component of Silymarin (SM), is a natural substance obtained
from the seeds of the milk thistle. SM contains up to 70% of SB as two isoforms: A and B. It has an antioxidant
and anti-inflammatory effect on hepatocytes and is known to inhibit cell proliferation, induce apoptosis, and
curb angiogenesis. SB has demonstrated activity against many cancers, such as skin, liver, lung, bladder, and
Methods: This review presents current knowledge of the use of SM in breast cancer, this being one of the most
common types of cancer in women. It describes selected molecular mechanisms of the action of SM; for example,
although SB influences both Estrogen Receptors (ER), α and β, it has opposite effects on the two. Its action on ERα
influences the PI3K/AKT/mTOR and RAS/ERK signaling pathways, while by up-regulating ERβ, it increases
the numbers of apoptotic cells. In addition, ERα is involved in SB-induced autophagy, while ERβ is not. Interestingly,
SB also inhibits metastasis by suppressing TGF-β2 expression, thus suppressing Epithelial to Mesenchymal
Transition (EMT). It also influences migration and invasive potential via the Jak2/STAT3 pathway.
Results: SB may be a promising enhancement of BC treatment: when combined with chemotherapeutic drugs
such as carboplatin, cisplatin, and doxorubicin, the combination exerts a synergistic effect against cancer cells.
This may be of value when treating aggressive types of mammary carcinoma.
Conclusion: Summarizing, SB inhibits proliferation, induces apoptosis, and restrains metastasis via several mechanisms.
It is possible to combine SB with different anticancer drugs, an approach that represents a promising therapeutic
strategy for patients suffering from BC.