The anti-oestrogen tamoxifen is the most commonly used treatment for patients with oestrogenreceptor (ER)-positive breast cancer. Although many patients benefit from tamoxifen in the adjuvant and metastatic settings, resistance is an important clinical problem. The target of tamoxifen in vivo is the ER. Over the last decade many advances have been made in our understanding of the biology of the ER which may help to explain how resistance to tamoxifen develops. Such mechanisms may include changes in the expression of ERa or ERb, alterations in co-regulatory proteins, and the influences of cellular kinase signal transduction pathways. The experimental and clinical evidence supporting these mechanisms of tamoxifen resistance are discussed in this review.

IMPORTANCE Current treatment cures most cases of early-stage, primary breast cancer. However, better techniques are required to identify which patients are at risk of relapse.OBJECTIVE To assess the clinical validity of molecular relapse detection with circulating tumor DNA (ctDNA) analysis in early-stage breast cancer. DESIGN, SETTING, AND PARTICIPANTSThis prospective, multicenter, sample collection, validation study conducted at 5 United Kingdom medical centers from November 24, 2011, to October 18, 2016, assessed patients with early-stage breast cancer irrespective of hormone receptor and ERBB2 (formerly HER2 or HER2/neu) status who were receiving neoadjuvant chemotherapy followed by surgery or surgery before adjuvant chemotherapy. The study recruited 170 women, with mutations identified in 101 patients forming the main cohort. Secondary analyses were conducted on a combined cohort of 144 patients, including 43 patients previously analyzed in a proof of principle study.INTERVENTIONS Primary tumor was sequenced to identify somatic mutations, and personalized tumor-specific digital polymerase chain reaction assays were used to monitor these mutations in serial plasma samples taken every 3 months for the first year of follow-up and subsequently every 6 months. MAIN OUTCOMES AND MEASURESThe primary end point was relapse-free survival analyzed with Cox proportional hazards regression models. RESULTSIn the main cohort of 101 female patients (mean [SD] age, 54 [11] years) with a median follow-up of 35.5 months (interquartile range, 27.9-43.0 months), detection of ctDNA during follow-up was associated with relapse (hazard ratio, 25.2; 95% CI, 6.7-95.6; P < .001). Detection of ctDNA at diagnosis, before any treatment, was also associated with relapse-free survival (hazard ratio, 5.8; 95% CI, 1.2-27.1; P = .01). In the combined cohort, ctDNA detection had a median lead time of 10.7 months (95% CI, 8.1-19.1 months) compared with clinical relapse and was associated with relapse in all breast cancer subtypes. Distant extracranial metastatic relapse was detected by ctDNA in 22 of 23 patients (96%). Brain-only metastasis was less commonly detected by ctDNA (1 of 6 patients [17%]), suggesting relapse sites less readily detectable by ctDNA analysis. CONCLUSIONS AND RELEVANCEThe findings suggest that detection of ctDNA during follow-up is associated with a high risk of future relapse of early-stage breast cancer. Prospective studies are needed to assess the potential of molecular relapse detection to guide adjuvant therapy.

The results show similar OS for patients diagnosed with BCP compared with nonpregnant patients. This information is important when patients are counseled and supports the option to start treatment with continuation of pregnancy.

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