Women who experience hot flashes, night sweats and joint pain when taking two common drugs to prevent breast cancer recurrence are less likely to have their disease return compared to women who do not develop side effects, an analysis of new research suggests.

Researchers found that the nine-year recurrence rate for women who reported the side effects within the first three months of taking either Tamoxifen or Arimidex was 18 per cent, compared to 23 per cent for women who did not experience side effects.

Women who developed joint symptoms three months after starting treatment had an even greater decrease in disease recurrence. Breast cancer recurred in 14 per cent of women with joint pain, compared to 23 per cent of women who did not experience joint pain.

The findings indicate that side effects may in fact be an indicator of the treatments' effectiveness and therefore may encourage patients to stick with their treatment despite their discomfort.

"Awareness of the relation between early treatment-emergent symptoms and beneficial response to therapy might be useful when reassuring patients who present with them, and might help to improve long-term treatment adherence when symptoms cannot be alleviated effectively," the authors concluded.

The researchers, from the Queen Mary School of Medicine and Dentistry in London, published their findings in the journal The Lancet Oncology.

Drugs like Tamoxifen and Arimidex are often given to breast cancer patients after they undergo conventional treatments such as radiation or chemotherapy to prevent the disease from recurring.

The medications block the effects of estrogen, which studies have shown can feed certain tumours.

Researchers said the next avenue of study will be to determine why the drugs lead to side effects in some patients and not in others.

Abstract:

Treatment-emergent endocrine symptoms and the risk of breast cancer recurrence: a retrospective analysis of the ATAC trial

Jack Cuzick, Ivana Sestak, David Cella, Lesley Fallowfield, on behalf of the ATAC Trialists' Group

Background When the mechanism of action behind treatment toxicity reflects the intended effect on the treatment target, the toxicity might be a useful marker for efficacy. During endocrine treatment of breast cancer, the occurrence of symptoms related to oestrogen depletion or oestrogen blockade might thus be a predictor of treatment effectiveness. In this retrospective analysis, the relation between the reported incidence of vasomotor or joint symptoms and breast cancer recurrence in the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial is assessed.

Methods Women with hormone-receptor-positive tumours who reported vasomotor or joint symptoms at the first follow-up visit (3 months) in the ATAC trial, (which assessed tamoxifen or anastrozole for adjuvant treatment of postmenopausal breast cancer), were compared with women without these symptoms to see if there was a relation between these symptoms and subsequent recurrence. The ATAC trial is registered as an International Standard Randomised Controlled Trial, number ISRCTN18233230.

Findings 1486 of 3964 (37-5%) eligible women reported newly emergent vasomotor symptoms at the 3-month follow-up visit and had lower subsequent recurrence than those who did not report these symptoms (223 during 10 752 women-years of follow-up vs 366 during 11 573 woman-years of follow-up, respectively; hazard ratio [HR] 0-84 [95% CI 0-71-1-00], p=0-04; adjusted for age, body-mass index, previous hormone-replacement therapy, nodal status, tumour size, and tumour grade). A greater decrease in breast-cancer recurrence was seen for the 1245 of 3964 (31-4%) eligible women who reported new joint symptoms at the 3-month follow-up visit compared with those not reporting these symptoms (158 during 9242 women-years of follow-up vs 366 during 11 573 women-years of follow-up; adjusted HR 0-60 [0-50-0-72], p<0-0001).

Interpretation The appearance of new vasomotor symptoms or joint symptoms within the first 3 months of treatment is a useful biomarker, suggesting a greater response to endocrine treatment compared with women without these symptoms. Awareness of the relation between early treatment-emergent symptoms and beneficial response to therapy might be useful when reassuring patients who present with them, and might help to improve long-term treatment adherence when symptoms cannot be alleviated effectively.