Breast cancer (BC) is the most common cancer (25% of all cancers) and the major cause of cancer mortality among women. The two prime strategies for the management of BC are locoregional treatment and systemic therapy based on the histological and molecular characteristics of BC.

      Immunohistochemistry (IHC) of BC is important for determining the treatment and predicting the prognosis. IHC characterization depends on the expression of biomarkers such as estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2).

      Approximately 70% of BC in women >50 years of age express ER and/or PgR, but not HER2, and are termed hormone receptor-positive (HR+ve) and HER2-ve BC. Metastatic BC patients with HR+ve and HER2 -ve BC have better survival rates than other sub-categories of advanced BC (aBC)(Onitilo et al., 2009).

      Endocrine therapy (ET) targeting the ER directly is the core treatment modality. However, it has been reported that 15-20% of tumors are intrinsically resistant to ET. Another 30-40% acquire resistance to ET over the years, resulting in relapse and metastasis of cancer that eventually leads to death.

       Ribociclib, a selective CDK4/6 inhibitor, is approved in India for the first-line treatment of women with HR+ve and HER2-ve locally advanced or metastatic BC in combination with an AI or fulvestrant as initial endocrine-based therapy or in women who have received prior ET (CDSCO).

      The clinical efficacy and safety of ribociclib has been well established by various clinical trials like MONALEESA-2 (Hortobagyi, 2016), MONALEESA-3 (Slamon, 2018) and MONALEESA-7 (Tripathy, 2018). However, the discussion is still ongoing on whether the use of CDK4/6 inhibitors as second-line or in subsequent lines of therapy provides an equal PFS compared to first-line usage.