Adding S-1 to hormonal therapy in patients with ER+ HER2- breast cancer

This study investigated whether adding oral S-1 (Teysuno) to hormonal therapy improved outcomes in patients with estrogen receptor (ER)-positive and HER2-negative primary breast cancer (BC). The data showed that the combination of S-1 with hormonal therapy could be a potential treatment option for these patients.

BC is classified into different subtypes depending on the presence or absence of certain receptors (proteins found on the surface of the cancer cells). ER (female sex hormone receptor)-positive and HER2 negative is a subtype of BC that tests positive for the ER and negative for the HER2 protein. This type of cancer accounts for 70% of all BCs. Patients with this subtype of BC commonly receive hormonal treatment which acts by decreasing the female hormone estrogen.

Fluoropyrimidines (FP) are anti-cancer drugs. S-1 is an FP prescribed orally and has been shown to be effective in the treatment of BC. However, it is not known if adding S-1 to hormonal treatment improves outcomes in patients with ER+ HER2- BC.

This study involved 1930 women with stage I-III ER+ HER2- invasive BC. 957 patients received S-1 plus hormonal therapy and 973 received hormonal therapy alone. The average follow-up time was 52.2 months.

87% of patients in the S-1 plus hormonal therapy group were alive after 5 years without signs of cancer compared with 82% in the hormonal therapy alone group. Cancer came back in other organs or tissues in 7% of the S-1 and hormonal therapy group compared to 10% of the hormonal therapy alone group.

31% of the S-1 group needed a reduction in the S-1 dose. The most common side effects were decreased white blood cells, diarrhea, and fatigue in both treatment groups.

This study concluded that the addition of oral S-1 to hormonal therapy improved the disease-free survival in patients with ER+ HER2- BC.

A longer follow-up period is necessary to measure the overall survival with this treatment option. The study was sponsored by Taiho Pharmaceutical, the manufacturers of S-1.