A new study from Japan provided firm evidence for the benefit of S-1 in treatment of patients with metastatic breast cancer (mBC).

The results, published online in Lancet Oncology by lead author Tsutomu Takashima and the SELECT BC group, show that, as first-line chemotherapy for mBC, S-1 produced similar efficacy as taxane therapy, with better health-related quality of life due to a different adverse-effect profile.1

The study was designed to demonstrate that S-1 (a combination oral drug containing fluorouracil, tegafur, gimeracil, and oteracil) was non-inferior to taxane therapy (a standard therapy for women with estrogen-receptor negative or endocrine-resistant mBC), with a primary endpoint of overall survival (OS).

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Investigators from the multicenter study enrolled women aged 20 to 75 years (n = 592), with human epidermal growth factor receptor (HER)2-negative, endocrine therapy-resistant mBC who had not previously received chemotherapy for their metastatic disease. Women with brain metastases were excluded.

Researchers randomly assigned patients to receive a standard taxane regimen (docetaxel or paclitaxel) or S-1 (twice daily x 28 days, followed by 14-day rest period). Treatment continued for 6 courses or until tumor progression or unacceptable toxicity occurred. The median age of women in the study was approximately 59 years; median follow-up was 34.6 months.

Median OS was similar between S-1 (35.0 months) and taxane therapy (37.2 months). Statistical analysis showed that S-1 was non-inferior to taxane (P for non-inferiority = .015). The median time to treatment failure was 8.0 months with S-1 and 8.9 months with taxanes. Median progression-free survival was 9.6 vs 11 months, respectively. The researchers also assessed safety and tolerability.

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The most common grade ≥ 3 events with S-1 or taxanes, respectively, were neutropenia (7% vs 3%), fatigue (3% vs 4%), and edema (< 1% vs 4%). Side effects commonly reported by patients as problematic—hair loss, edema, and peripheral neuropathies—were rare with S-1 and occurred at significantly lower rates than with taxanes.