According to the 2019 national cancer registration statistics by the Ministry of Health and Welfare and Korea Central Cancer Registry, the annual number of newly diagnosed breast cancer patients exceeded 20,000 in 2016. As of 2019, breast cancer ranked first among cancer in women in Korea.

Fortunately, the five-year and the 10-year survival rates of breast cancer in patients diagnosed between 2015 and 2019 were 93.6 percent and 88.6 percent, respectively. These survival rates are higher than those of other major cancer. So, breast cancer patients can expect a positive prognosis.

However, the five-year survival rate of metastatic breast cancer that spread to other organs, classified as stage 4, was only 42.6 percent.

The treatment goal of metastatic breast cancer, which has a relatively poor prognosis, is to delay cancer progression as much as possible, prolong survival, and improve quality of life during treatment.

In the past, there were not many treatment options to choose from.

Recently, however, various treatment options such as targeted therapy and endocrine therapy have emerged. It is now possible to treat metastatic breast cancer depending on the characteristics of cancer, and the survival rate and quality of life of patients have improved significantly.

Metastatic breast cancer can be divided into HR-negative, HER2-negative, HR-positive, and HER2-positive cases depending on the treatment regimen. In breast cancer with HER-2 gene amplification, targeted therapy that inhibits the HER-2 gene improved the survival rate and quality of life dramatically.

HR-positive/HER2-negative metastatic breast cancer patients showed unsatisfactory survival rates and the period of chemotherapy was short, with conventional endocrine therapy alone. So, many patients experienced adverse reactions early because of early chemotherapy.

Recently, however, a CDK 4&6 inhibitor, targeted therapy, emerged. When it was used in combination with endocrine therapy, treatment outcomes improved.

The use of a CDK 4&6 inhibitor and endocrine therapy together maintained remission for a longer time than endocrine alone and extended the period of chemotherapy. The combo also delayed the experience of side effects of chemotherapy, raising expectations among metastatic breast cancer patients and physicians.

Before the arrival of CDK 4&6 inhibitors, endocrine therapy or chemotherapy was mainly used considering tumor characteristics and patient conditions. However, some patients show low responses to endocrine therapy, and resistance develops with continued use. As the disease progresses, chemotherapy affects normal cells, causing severe side effects throughout the body, making it difficult for patients to lead daily life.

CDK 4&6 inhibitors combined with endocrine therapy have demonstrated clinical efficacy for patients with HR-positive/HER2-negative metastatic breast cancer. Clinical studies have shown that the combo of a CDK 4&6 inhibitor and endocrine therapy contributed to improving patients' quality of life by prolonging overall survival (OS) and progression-free survival (PFS) and delaying the start of chemotherapy.

Authorized CDK 4&6 inhibitors in Korea include palbociclib, ribociclib, and abemaciclib. Among them, abemaciclib can be taken continuously without a withdrawal period. This lowers the possibility of misuse for patients taking other medications for underlying diseases or elderly patients living alone.

Abemaciclib also demonstrated a benefit in prolonging the median PFS even in metastatic breast cancer with a poor prognosis.

When I meet patients with liver metastasis, high tumor grade, or short recurrence period, or those with negative progesterone receptors, or those with metastasis to organs other than bone, I have no choice but to think carefully and realistically about which treatment I should prescribe.

Abemaciclib was clinically beneficial in these patients in sub-analysis studies.

This is why I, as a doctor, welcome CDK 4&6 inhibitors as a new treatment option.

CDK 4&6 inhibitors are covered by health insurance for metastatic breast cancer if conditions are met, allowing patients to focus on treatment while easing their financial burden. The U.S. National Comprehensive Cancer Network (NCCN) also recommends combination therapy with a CDK 4&6 inhibitor and an aromatase inhibitor or fulvestrant as “Category 1” among treatments for HR-positive/HER2-negative metastatic breast cancer.

Metastatic breast cancer patients feel more frustrated when they learn the metastasis and recurrence than when they were first diagnosed with cancer.

However, they should not give up treatment or be afraid of the treatment process.

Many good treatments have been developed now and it has become more important to decide which treatment to use, in consultation with a doctor.

It is important not only to choose the optimal treatment considering the survival rate, quality of life, safety management, and adverse event risks but to consult with professional healthcare providers to actively receive treatment without losing hope.