Adding S-1 to post-operative endocrine therapy in patients with hormone receptor-positive HER2-negative breast cancer

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Published: 19 Dec 2019
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Prof Masakazu Toi - Kyoto University, Kyoto, Japan

Prof Masakazu Toi speaks to ecancer at the 2019 San Antonio Breast Cancer Symposium about the combination of S-1 with endocrine therapy for patients with hormone receptor-positive, HER2-negative breast cancer.

He describes the design of the trial which evaluated endocrine treatment plus S-1 (an an oral fluoropyrimidine-based drug), versus endocrine treatment alone.

Prof Toi outlines the main results from this study and the action of S-1.

For the future, he believes this study should be expanded and include additional countries and genomic testing will be incorporated to select patients.

Watch the press conference here

Read more about the study here

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We conducted a clinical trial, adjuvant trial, focussing on the luminal disease patients having intermediate risk or high risk. We designed the trial comparing endocrine treatment alone and plus S-1 oral 5FU and continuously treated for one year of time the three week regimen after the adjuvant chemotherapy or after neoadjuvant chemotherapy.

What were the results?

Actually 1,930 patients were enrolled in this trial and that got very nice results. The hazard ratio was 0.63 in favour for the S-1 treatment arm compared with the endocrine treatment alone.

Can you tell us about S-1?

S-1 is the biochemical modulation of three different agents. The core agent is tegafur, the other two agents are increasing the efficacy of the drug, the 5FU, and also decreasing the toxicity, particularly GI toxicity. It’s a very nice formulation and it is known to be active in metastatic disease situation treatment.

Is this used globally?

Yes, it’s quite widely used in Japan. It’s a broad indication for multiple types of cancers. It is also approved in some other countries but still somehow limited.

What are the main conclusions to take away from this study?

This is just a Japanese, a one country, trial that we need to study more in other countries as well. So we need more expanded studies etc. So more investigations are actually needed.

What does the toxicity profile look like?

We have seen a higher incidence in bone marrow toxicity, particularly the neutrophil counts and also the GI toxicity is significantly higher in the S-1 arm. Additionally, the hyperpigmentation is also frequent, it’s about 50% of the patients experience this toxicity in the S-1 arm. But overall it’s quite manageable and the safety profile is just as expected.

Could you incorporate genomic testing to select patients?

We have incorporated to make a risk assessment we have incorporated. One is clinical pathological, clinical staging, and the Ki67 progression marker assessment and also the OncotypeDX test is incorporated. But for OncotypeDX assessing is quite a limited number of the cases measured by OncotypeDX assessing.

What is the incidence and treatment landscape like for breast cancer patients in Japan?

It’s very unfortunate, the incidence of breast cancer is still increasing quite rapidly. It’s been doubling for fifty years’ time. We don’t know why. But the overall outcomes of the treatments, also it has improved. So the incidence is increasing, the mortality rate is somehow going down. That’s the situation in Japan.