Letrozole Plus Metronomic Capecitabine as First-line Treatment for Patients With Recurrent or Metastatic Breast Cancer

Breast cancer is recognized as the commonest cancer in females, and the second commonest malignant tumor, after lung cancer, in overall figures worldwide. In 2021, an estimated 281,550 new cases of invasive breast cancer are expected to be diagnosed in women in the U.S., along with 49,290 new cases of non-invasive (in situ) breast cancer. About 43,600 women in the U.S. are expected to die in 2021 from breast cancer. Death rates have been steady in women under 50 since 2007, but have continued to drop in women over 50. The overall death rate from breast cancer decreased by 1% per year from 2013 to 2018. These decreases are thought to be the result of treatment advances and earlier detection through screening. According to the World Health Organization, breast cancer became the most common cancer globally as of 2021, accounting for 12% of all new annual cancer cases worldwide. Breast cancer is increasingly recognized as a heterogeneous disease exhibiting substantial differences concerning biological behavior and requiring distinct therapeutic interventions. There has been a continuous decline in mortality over recent years due to improvements in early diagnosis and the increased availability of more effective treatments. However, despite these improvements, The treatment of hormone receptor-positive metastatic breast cancer (MBC) who developed disease progression on first-line hormonal treatment that included aromatase inhibitors (AI) represents a challenge as those patients ultimately develop resistant disease unresponsive to standard lines of estrogen receptors (ER) blockade. Capecitabine is an oral chemotherapy that mimics continuous infusion of 5-FU with known activity in MBC. It might be preferred because of its tolerability and relatively lower toxicity than other chemotherapeutic agents. Metronomic chemotherapy is defined as the frequent (daily, many times a week, or weekly) or continuous administration of low dose chemotherapeutic agents, without prolonged drug-free intervals. This way of administration improves the antiangiogenic activity of chemotherapy. Another important advantage of this approach is the significant reduction in toxicity. Capecitabine's pharmacokinetics and high safety profile make it a suitable drug for metronomic administration. Many studies reported that the overall response rate can be improved by (15.8-21.7%) when metronomic chemotherapy is combined with aromatase inhibitors. This combination can also decrease the level of both the Ki-67 index and VEGF-A significantly in the tumor tissue. It was reported that the patients who received letrozole plus metronomic chemotherapy achieved a higher overall response rate (ORR) than those who received letrozole alone (87.7% vs 71.9% respectively.