Breast care and research colleagues look into side effects of endocrine treatment

A specialist breast cancer nurse has teamed up with our research team to explore how changes in the brand of endocrine medication – taken to help prevent breast cancer from returning – may affect the side effects patients experience.

Adjuvant endocrine treatment is commonly prescribed to reduce the risk of breast cancer recurring. However, it can bring challenging side effects, including menopausal symptoms, which many women find difficult to manage.

The national study, called SWITCH, is funded by the National Institute for Health and Care Research and sponsored by University College London.

Becky Laney, one of our advanced nurse practitioners at Yeovil Hospital who’s also our trust’s principal investigator for the study, says patients often tell her that changing to a different medication brand has either improved or worsened their side effects.

“The change in medication brand is a common theme that my patients have brought up with me over the years,” she says.

“When I told them we were getting involved in a national study looking into whether certain brands cause more side effects than others, so many people were eager to take part."

Becky says patients often feel strongly about which brand works best for them. “If a patient feels a particular brand suits them, they’ll often try to hunt it down in local pharmacies… but this can be difficult, and sometimes their preferred brand is impossible to find.

“Most women won’t receive the same brand every time, and although they may feel better on one, they’re not guaranteed it at their next prescription.

“We’ve even had women return to us for help when their GP hasn’t been able to source a particular brand, and sadly we’ve seen others stop treatment altogether because they can’t cope with the side effects of a different one.”

Becky adds that although there has been research into managing endocrine side effects, there has been little investigation into whether different brands cause different levels of symptoms.

“The SWITCH study focuses on the impact of brand changes on women’s quality of life, their ability to tolerate treatment, and the severity of any side effects,” she continues.

“We know that a significant number of women stop taking their endocrine treatment because of the side effects, and unfortunately, this is known to increase the risk of the cancer coming back.

“The aim of the SWITCH study is to understand the impact that brand changes truly have on patients.”

Zenaida Dagutao, one of our clinical research assistant practitioners, explains how the study works in practice.

“Patients who join the study are followed for nine months and complete a weekly survey, which takes around three to five minutes,” she says.

“The main survey asks them to record any side effects they’ve experienced. There’s also a short monthly survey that asks about whether participants been taking their tablets regularly and whether they’ve picked up a new brand.

“At the end of the nine months, participants complete one last brief survey about their experience - which can be done via a mobile app.”

While we have now reached our initial recruitment target, the national study centre has asked the team to continue recruiting until the end of this month (February 2026), but now specifically focusing on patients from global majority backgrounds - a group currently underrepresented in the study.

“Once recruitment closes and all our patients have completed their nine months in the study, we’ll be eagerly waiting to hear the results once the national data analysis is completed,” Zenaida concludes.