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Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) consisting of a humanised, anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody covalently linked to a topoisomerase I inhibitor cytotoxic payload (DXd). The high drug-to-antibody ratio (8:1) ensures a high DXd concentration is delivered to target tumour cells, following internalisation of T-DXd and subsequent cleavage of its tetrapeptide-based linker. DXd's membrane-permeable nature enables it to cross cell membranes and potentially exert antitumour activity on surrounding tumour cells regardless of HER2 expression. T-DXd's unique mechanism of action is reflected in its efficacy in clinical trials in patients with HER2-positive advanced breast cancer (in heavily pretreated populations and in those previously treated with a taxane and trastuzumab), as well as HER2-low metastatic breast cancer. Thus, ADCs such as T-DXd have the potential to change the treatment paradigm of targeting HER2 in metastatic breast cancer, including eventually within the adjuvant/neoadjuvant setting. [Display omitted] • Antibody-drug conjugates have significantly improved breast cancer (BC) treatment. • Trastuzumab deruxtecan's (T-DXd) structure allows large payload delivery to targets. • T-DXd has demonstrated unprecedented efficacy in patients with HER2+ advanced BC. • T-DXd has significantly improved survival rates in heavily pretreated BC patients. • T-DXd may change the treatment paradigm of targeting HER2 in metastatic BC. [ABSTRACT FROM AUTHOR]

Objective To examine the influence of physical activity on breast cancer risk and evaluate whether adherence to international recommendations is associated with a decreased risk. Methods This is a multicenter matched case-control study where 698 pairs completed a physical activity questionnaire. Recreational physical activity during the last year was quantified in metabolic equivalent hours per week (MET-h/week) and categorized in activities of moderate (3.0–5.9 MET) and vigorous (> 6 MET) intensity. The adherence to World Cancer Research Fund and the American Institute for Cancer Research recommendation was also assessed. The association with breast cancer risk, overall and by pathologic subtype, was evaluated using conditional and multinomial logistic regression models. Results Mean MET-h/week was 16.6 among cases and 20.4 among controls. Premenopausal breast cancer risk decreased by 5% ( P = 0.007) for every 6 MET-h/week increase in energy expenditure. By contrast, postmenopausal women needed to do more intense exercise to observe benefits. The protection was more pronounced for nulliparous women, as well as for hormone receptor positive and HER2 + tumors. Physically inactive women displayed a 71% increased risk when compared with those who met the international recommendation ( P = 0.001). Finally, women who were inactive during the previous year, regardless of the overall physical activity reported in previous periods, showed an increased risk when compared to always active women. Conclusions Women who report adherence to international physical activity recommendations entail a significant decrease in risk for all pathologic breast cancer subtypes. This is of particular interest in Spain, where a significant increase in overweight and obesity in recent decades is observed. [ABSTRACT FROM AUTHOR]

Purpose: Improved understanding of risk of recurrence (ROR) is needed to reduce cases of recurrence and more effectively treat breast cancer patients. The purpose of this study was to examine how a gene-expression profile (GEP), identified by Prosigna, influences physician adjuvant treatment selection for early breast cancer (EBC) and the effects of this influence on optimizing adjuvant treatment recommendations in clinical practice. Methods: A prospective, observational, multicenter study was carried out in 15 hospitals across Spain. Participating medical oncologists completed pre-assessment, post-assessment, and follow-up questionnaires recording their treatment recommendations and confidence in these recommendations, before and after knowing the patient's ROR. Patients completed questionnaires on decision-making, anxiety, and health status. Results: Between June 2013 and January 2014, 217 patients enrolled and a final 200 were included in the study. Patients were postmenopausal, estrogen receptor positive, human epidermal growth hormone factor negative, and node negative with either stage 1 or stage 2 tumors. After receiving the GEP results, treatment recommendations were changed for 40 patients (20%). The confidence of medical oncologists in their treatment recommendations increased in 41.6% and decreased in 6.5% of total cases. Patients reported lower anxiety after physicians made treatment recommendations based on the GEP results (p50.05). Conclusions: Though this study does not include evaluation of the impact of GEP on long-term outcomes, it was found that GEP results influenced the treatment decisions of medical oncologists and their confidence in adjuvant therapy selection. Patients' anxiety about the selected adjuvant therapy decreased with use of the GEP. [ABSTRACT FROM AUTHOR]

Background: A regimen of docetaxel, doxorubicin, and cyclophosphamide (TAC) is superior to a regimen of fluorouracil, doxorubicin, and cyclophosphamide (FAC) when used as adjuvant therapy in women with node-positive breast cancer. The value of taxanes in the treatment of node-negative disease has not been determined. Methods: We randomly assigned 1060 women with axillary-node–negative breast cancer and at least one high-risk factor for recurrence (according to the 1998 St. Gallen criteria) to treatment with TAC or FAC every 3 weeks for six cycles after surgery. The primary end point was disease-free survival after at least 5 years of follow-up. Secondary end points included overall survival and toxicity. Results: At a median follow-up of 77 months, the proportion of patients alive and disease-free was higher among the 539 women in the TAC group (87.8%) than among the 521 women in the FAC group (81.8%), representing a 32% reduction in the risk of recurrence with TAC (hazard ratio, 0.68; 95% confidence interval [CI], 0.49 to 0.93; P=0.01 by the log-rank test). This benefit was consistent, regardless of hormone-receptor status, menopausal status, or number of high-risk factors. The difference in survival rates (TAC, 95.2%; FAC, 93.5%) was not significant (hazard ratio, 0.76; 95% CI, 0.45 to 1.26); however, the number of events was small (TAC, 26; FAC, 34). Rates of grade 3 or 4 adverse events were 28.2% with TAC and 17.0% with FAC (P<0.001). Toxicity associated with TAC was diminished when primary prophylaxis with granulocyte colony-stimulating factor was provided. Conclusions: As compared with adjuvant FAC, adjuvant TAC improved the rate of disease-free survival among women with high-risk, node-negative breast cancer. (Funded by GEICAM and Sanofi-Aventis; ClinicalTrials.gov number, NCT00121992.) N Engl J Med 2010;363:2200-10. [ABSTRACT FROM AUTHOR]

The taxanes, paclitaxel and docetaxel, are an important class of antineoplastic agents with relevant clinical activity in both early and advanced breast cancer. Nanoparticle albumin-bound paclitaxel (Abraxane®) is a 130-nm particle cremophor-free formulation of paclitaxel. Exploiting endogenous albumin pathways and avoiding solvent-based toxicities, nab-paclitaxel allows higher intratumor concentrations of paclitaxel through gp60 mediated endothelial transcytosis. Also, because it is free solvents, nab-paclitaxel offers shorter infusions and easily administration with no premedication and special infusions sets. In a phase III randomized trial, nab- paclitaxel at 260 mg/m2 every 3 weeks seems to have a superior therapeutic index than Cr-El paclitaxel, with a higher response rate and longer time to progression and with less toxicity, except peripheral neuropathy. Based on these results, nab-paclitaxel was approved for the treatment of metastatic breast cancer in patients who have failed first-line treatment for metastatic disease and for whom standard; anthracycline containing therapy is not indicated. The results of the comparison of three doses of nab-paclitaxel with docetaxel in a randomized phase II trial suggest a superior efficacy and safety of weekly nab-paclitaxel compared with 3-weekly docetaxel. All the available data suggest the superior therapeutic index of nab-paclitaxel compared with both docetaxel and Cr-EL paclitaxel. Weekly nab-paclitaxel may be an adequate alternative to classic formulations of taxanes in the treatment of patients with metastatic breast cancer. [ABSTRACT FROM AUTHOR]

Summary: Background: We aimed to compare the additional benefit of gemcitabine when combined with vinorelbine above that of standard vinorelbine treatment in patients with metastatic breast cancer. Methods: In this phase III, multicentre, open-label, randomised study, 252 women with locally recurrent and metastatic breast cancer who had been pretreated with anthracyclines and taxanes were randomly assigned single-agent vinorelbine (30 mg/m2, days 1 and 8) or gemcitabine plus vinorelbine (1200/30 mg/m2, days 1 and 8). Both study treatments were administered intravenously every 21 days until disease progression, unacceptable toxic effects, or stoppage at the request of investigator or patient. The primary endpoint was median progression-free survival. Secondary objectives included assessments of response rate, disease duration, overall survival, and characterisation of the toxicity profiles of both regimens. This study is registered with ClinicalTrials.gov, number NCT00128310. Findings: Between 2001 and 2005, 252 women were recruited and randomised for treatment. One of these patients was ineligible. Prognostic factors were well balanced between treatment groups (median number of metastatic sites in combination group 2 (range 0–5) and in vinorelbine group 2 (range 1–6); visceral disease in 76% and 75% of patients, respectively). Median progression-free survival was 6·0 months (95% CI 4·8–7·1) for patients given gemcitabine plus vinorelbine and 4·0 months (2·9–5·1) for those assigned vinorelbine; there was 1·9 months of difference (hazard ratio 0·66 [0·50–0·88]; p=0·0028). Overall survival was 15·9 months (12·6–19·1) for the gemcitabine plus vinorelbine group and 16·4 months (11·6–21·0) for the vinorelbine group; there was 0·5 months of difference (hazard ratio 1·04 [0·78–1·39]; p=0·8046). Objective response rates were 36% for patients assigned gemcitabine plus vinorelbine (n=45) and 26% for those assigned vinorelbine (n=33) (p=0·093). Grade 3 or 4 neutropenia was reported in 75 (61% [52–70]) of the participants assigned gemcitabine plus vinorelbine, compared with 55 (44% [35–53]) of those assigned vinorelbine alone (p=0·0074). Febrile neutropenia occurred in 13 (11%) of those assigned gemcitabine plus vinorelbine, and in seven (6%) of those assigned vinorelbine alone (p=0·15). Incidences of grade 3 or 4 non-haematological toxic effects were similar between the two treatment groups. Interpretation: Patients with metastatic breast cancer assigned gemcitabine and vinorelbine had better progression-free survival compared with those assigned vinorelbine alone. However, this finding did not translate into a difference in overall survival. Although toxicity was manageable, patients in the combined group had more haematological toxic effects. These factors should be taken into account when deciding which chemotherapy patients should receive. [Copyright &y& Elsevier]

Purpose: To compare the cardiovascular fitness of breast cancer (BC) survivors with an active lifestyle to those with a sedentary lifestyle. Methods: A cross-sectional study was conducted. Participants were classified into four groups: two groups of active women who performed more than 150 min/week of physical exercise, active with BC (Act-BCW) and active without BC (Act-HW); and two groups of sedentary women who performed less than 90 min/week of physical exercise, sedentary with BC (Sed-BCW) and sedentary without BC (Sed-HW). VO2max was estimated by the 6-min walking test (6MWT); speed, isometric strength, lower body maximum strength, explosive strength, balance, and body composition were also measured. ANOVA was used to analyze group differences and post hoc comparisons were developed with the Bonferroni test. Results: A total of 92 women were recruited. Significant differences were found in VO2max between the Act-BCW and Sed-BCW groups (MeanDif = 5.86, p < 0.001). No differences in VO2max were observed between the active groups (MeanDif = 0.42, p = 0.753). Related body composition and fat mass levels were significantly lower in the Act-BCW group than in the sedentary groups (Sed-BCW MeanDif = − 6.78; p = 0.012; and Sed-HW MeanDif = − 12.07; p < 0.001). Conclusions: Women who are Act-BCW can achieve similar values in physical condition as women who are Act-HW and have better values than women who are sedentary. Furthermore, our results suggest than physical activity level may have a greater impact in body composition than a previous history of BC. [ABSTRACT FROM AUTHOR]

Background: Previous studies have independently validated the prognostic relevance of residual cancer burden (RCB) after neoadjuvant chemotherapy. We used results from several independent cohorts in a pooled patient-level analysis to evaluate the relationship of RCB with long-term prognosis across different phenotypic subtypes of breast cancer, to assess generalisability in a broad range of practice settings.Methods: In this pooled analysis, 12 institutes and trials in Europe and the USA were identified by personal communications with site investigators. We obtained participant-level RCB results, and data on clinical and pathological stage, tumour subtype and grade, and treatment and follow-up in November, 2019, from patients (aged ≥18 years) with primary stage I-III breast cancer treated with neoadjuvant chemotherapy followed by surgery. We assessed the association between the continuous RCB score and the primary study outcome, event-free survival, using mixed-effects Cox models with the incorporation of random RCB and cohort effects to account for between-study heterogeneity, and stratification to account for differences in baseline hazard across cancer subtypes defined by hormone receptor status and HER2 status. The association was further evaluated within each breast cancer subtype in multivariable analyses incorporating random RCB and cohort effects and adjustments for age and pretreatment clinical T category, nodal status, and tumour grade. Kaplan-Meier estimates of event-free survival at 3, 5, and 10 years were computed for each RCB class within each subtype.Findings: We analysed participant-level data from 5161 patients treated with neoadjuvant chemotherapy between Sept 12, 1994, and Feb 11, 2019. Median age was 49 years (IQR 20-80). 1164 event-free survival events occurred during follow-up (median follow-up 56 months [IQR 0-186]). RCB score was prognostic within each breast cancer subtype, with higher RCB score significantly associated with worse event-free survival. The univariable hazard ratio (HR) associated with one unit increase in RCB ranged from 1·55 (95% CI 1·41-1·71) for hormone receptor-positive, HER2-negative patients to 2·16 (1·79-2·61) for the hormone receptor-negative, HER2-positive group (with or without HER2-targeted therapy; p<0·0001 for all subtypes). RCB score remained prognostic for event-free survival in multivariable models adjusted for age, grade, T category, and nodal status at baseline: the adjusted HR ranged from 1·52 (1·36-1·69) in the hormone receptor-positive, HER2-negative group to 2·09 (1·73-2·53) in the hormone receptor-negative, HER2-positive group (p<0·0001 for all subtypes).Interpretation: RCB score and class were independently prognostic in all subtypes of breast cancer, and generalisable to multiple practice settings. Although variability in hormone receptor subtype definitions and treatment across patients are likely to affect prognostic performance, the association we observed between RCB and a patient's residual risk suggests that prospective evaluation of RCB could be considered to become part of standard pathology reporting after neoadjuvant therapy.Funding: National Cancer Institute at the US National Institutes of Health. [ABSTRACT FROM AUTHOR]

Purpose: To determine the frequency of breast cancer (BC) patients with hereditary risk features in a wide retrospective cohort of patients in Spain. Methods: a retrospective analysis was conducted from 10,638 BC patients diagnosed between 1998 and 2001 in the GEICAM registry “El Álamo III”, dividing them into four groups according to modified ESMO and SEOM hereditary cancer risk criteria: Sporadic breast cancer group (R0); Individual risk group (IR); Familial risk group (FR); Individual and familial risk group (IFR) with both individual and familial risk criteria. Results: 7,641 patients were evaluable. Of them, 2,252 patients (29.5%) had at least one hereditary risk criteria, being subclassified in: FR 1.105 (14.5%), IR 970 (12.7%), IFR 177 (2.3%). There was a higher frequency of newly diagnosed metastatic patients in the IR group (5.1% vs 3.2%, p = 0.02). In contrast, in RO were lower proportion of big tumors (> T2) (43.8% vs 47.4%, p = 0.023), nodal involvement (43.4% vs 48.1%, p = 0.004) and lower histological grades (20.9% G3 for the R0 vs 29.8%) when compared to patients with any risk criteria. Conclusions: Almost three out of ten BC patients have at least one hereditary risk cancer feature that would warrant further genetic counseling. Patients with hereditary cancer risk seems to be diagnosed with worse prognosis factors. [ABSTRACT FROM AUTHOR]

Background Diet is a key modifiable risk for many chronic diseases, but it remains unclear whether dietary patterns from one study sample are generalizable to other independent populations. Objective The primary objective of this study was to assess whether data-driven dietary patterns from one study sample are applicable to other populations. The secondary objective was to assess the validity of two criteria of pattern similarity. Methods Six dietary patterns—Western (n=3), Mediterranean, Prudent, and Healthy— from three published studies on breast cancer were reconstructed in a case-control study of 973 breast cancer patients and 973 controls. Three more internal patterns (Western, Prudent, and Mediterranean) were derived from this case-control study’s own data. Statistical analysis Applicability was assessed by comparing the six reconstructed patterns with the three internal dietary patterns, using the congruence coefficient (CC) between pattern loadings. In cases where any pair met either of two commonly used criteria for declaring patterns similar (CC ≥0.85 or a statistically significant [ P <0.05] Pearson correlation), then the true similarity of those two dietary patterns was double-checked by comparing their associations to risk for breast cancer, to assess whether those two criteria of similarity are actually reliable. Results Five of the six reconstructed dietary patterns showed high congruence (CC >0.9) to their corresponding dietary pattern derived from the case-control study’s data. Similar associations with risk for breast cancer were found in all pairs of dietary patterns that had high CC but not in all pairs of dietary patterns with statistically significant correlations. Conclusions Similar dietary patterns can be found in independent samples. The P value of a correlation coefficient is less reliable than the CC as a criterion for declaring two dietary patterns similar. This study shows that diet scores based on a particular study are generalizable to other populations. [ABSTRACT FROM AUTHOR]

Purpose: Zoledronic acid (ZA) or denosumab treatment reduces skeletal-related events; however, the safety of prolonged therapy has not been adequately studied. Here, we describe safety results of extended denosumab therapy in patients with bone metastases from the open-label extension phase of two phase 3 trials.Methods: Patients with metastatic breast or prostate cancer received subcutaneous denosumab 120 mg Q4W or intravenous ZA 4 mg Q4W in a double-blinded fashion. Denosumab demonstrated superior efficacy in the blinded treatment phase; thus, patients were offered open-label denosumab for up to an additional 2 years.Results: Cumulative median (Q1, Q3) denosumab exposure was 19.1 (9.2, 32.2) months in the breast cancer trial (n = 1019) and 12.0 (5.6, 21.3) months in the prostate cancer trial (n = 942); 295 patients received denosumab for >3 years. No new safety signals were identified during the open-label phase, or among patients who switched from ZA to denosumab. During the blinded treatment phase, exposure-adjusted subject incidences of osteonecrosis of the jaw (ONJ) were 49 (1.9%) and 31 (1.2%) in the denosumab and ZA groups, respectively. In total, 32 (6.9%) and 25 (5.5 %) new cases of ONJ (not adjusted for exposure) were reported for patients continuing and switching to denosumab, respectively. The incidences of hypocalcemia were 4.3 and 3.1%, in patients continuing and switching to denosumab, respectively.Conclusion: These results describe the safety profile of denosumab after long-term exposure, or after switching to denosumab from ZA. No new safety signals were identified. Hypocalcemia rates were similar in the blinded treatment and open-label phases. ONJ rates increased with increasing exposure to antiresorptives, consistent with previous reports. [ABSTRACT FROM AUTHOR]

Summary: Background: Patients with isolated locoregional recurrences (ILRR) of breast cancer have a high risk of distant metastasis and death from breast cancer. We aimed to establish whether adjuvant chemotherapy improves the outcome of such patients. Methods: The CALOR trial was a pragmatic, open-label, randomised trial that accrued patients with histologically proven and completely excised ILRR after unilateral breast cancer who had undergone a mastectomy or lumpectomy with clear surgical margins. Eligible patients were enrolled from hospitals worldwide and were centrally randomised (1:1) to chemotherapy (type selected by the investigator; multidrug for at least four courses recommended) or no chemotherapy, using permuted blocks, and stratified by previous chemotherapy, oestrogen-receptor and progesterone-receptor status, and location of ILRR. Patients with oestrogen-receptor-positive ILRR received adjuvant endocrine therapy, radiation therapy was mandated for patients with microscopically involved surgical margins, and anti-HER2 therapy was optional. The primary endpoint was disease-free survival. All analyses were by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00074152. Findings: From Aug 22, 2003, to Jan 31, 2010, 85 patients were randomly assigned to receive chemotherapy and 77 were assigned to no chemotherapy. At a median follow-up of 4·9 years (IQR 3·6–6 ·0), 24 (28%) patients had disease-free survival events in the chemotherapy group compared with 34 (44%) in the no chemotherapy group. 5-year disease-free survival was 69% (95% CI 56–79) with chemotherapy versus 57% (44–67) without chemotherapy (hazard ratio 0·59 [95% CI 0·35–0·99]; p=0·046). Adjuvant chemotherapy was significantly more effective for women with oestrogen-receptor-negative ILRR (pinteraction=0·046), but analyses of disease-free survival according to the oestrogen-receptor status of the primary tumour were not statistically significant (pinteraction=0·43). Of the 81 patients who received chemotherapy, 12 (15%) had serious adverse events. The most common adverse events were neutropenia, febrile neutropenia, and intestinal infection. Interpretation: Adjuvant chemotherapy should be recommended for patients with completely resected ILRR of breast cancer, especially if the recurrence is oestrogen-receptor negative. Funding: US Department of Health and Human Services, Swiss Group for Clinical Cancer Research (SAKK), Frontier Science and Technology Research Foundation, Australian and New Zealand Breast Cancer Trials Group, Swedish Cancer Society, Oncosuisse, Cancer Association of South Africa, Foundation for Clinical Research of Eastern Switzerland (OSKK), Grupo Español de Investigación en Cáncer de Mama (GEICAM), and the Dutch Breast Cancer Trialists' Group (BOOG). [ABSTRACT FROM AUTHOR]

Purpose: Dose-limiting neuropathy is a major adverse event associated with most of the microtubule-stabilizing agent-based chemotherapy regimens. Ixabepilone, a semisynthetic analogue of the natural epothilone B, has activity against a wide range of tumor types. Peripheral neuropathy (PN), associated with ixabepilone treatment, is usually mild to moderate, predominantly sensory and cumulative. Preclinical studies demonstrate that ixabepilone and taxanes produce a similar neurotoxicity profile. Methods: We searched databases of phase II/III clinical trials involving patients receiving ixabepilone as a monotherapy or in combination with capecitabine for incidences of neuropathy. Potential risk factors for grade 3/4 PN were identified by a Cox regression analysis on a dataset of 1,540 patients with different tumor types across multiple studies. Results: Rates for incidence of ixabepilone-induced severe PN (Common Terminology Criteria for Adverse Events grade 3/4) ranged from 1% in early untreated breast cancer up to 24% in heavily pretreated metastatic breast cancer; grade 4 PN was rare (≤1%). Common symptoms included numbness, paresthesias, and sometimes dysesthesias. Cox regression analysis identified only preexisting neuropathy as a risk factor for increased ixabepilone-associated PN. The management of PN has been primarily through dose adjustments (dose delays and/or dose reduction). Patients had resolution of their neuropathy within a median time of 5 to 6 weeks. Conclusions: PN is a dose-limiting toxicity associated with ixabepilone treatment, is reversible in most patients, and can be managed with dose reduction and delays. [ABSTRACT FROM AUTHOR]

Genetic background is an important determinant of the etiology of breast cancer and varies between subtle changes in risk caused by common genetic variants and high-risk susceptibility genes such as BRCA1 and BRCA2. We present an updated overview of the most important molecular and clinical features of the genes involved in breast cancer. We focus on the well-known BRCA1 and BRCA2 genes and on the management of patients in terms of risk assessment, screening, prevention, and emerging therapies based on BRCA molecular pathology. We also address other recently discovered susceptibility genes (eg, CHEK2, RAD51C, PALB2, and BRIP1) and other hereditary syndromes in which breast cancer frequently appears such as Li-Fraumeni Syndrome, Cowden Syndrome, Peutz Jeghers Syndrome, hereditary diffuse gastric cancer, and Lynch Syndrome. Finally, we briefly analyze the new concept of high-prevalence-low-penetrance genetic variants, which has arisen from genome-wide associated studies. [ABSTRACT FROM AUTHOR]

Simple Summary: Liquid biopsy appears as a feasible opportunity to complement tissue biopsy within breast cancer research and real-time monitoring of the disease. In this review, we not only summaries cur-rent trends in the study of CTCs as a potential biomarker of response to systemic therapies but also the technical challenges for their implementation in clinical practice, including the role of free circulating DNA and new approaches based on the isolation of CTCs from body fluids. We also highlight the importance of a consensus on the standardization of liquid biopsy methodologies as a fundamental requirement for their implementation in clinical practice. Breast cancer is the most common neoplasm in women worldwide. Tissue biopsy, currently the gold standard to obtain tumor molecular information, is invasive and might be affected by tumor heterogeneity rendering it incapable to portray the complete dynamic picture by the absence of specific genetic changes during the evolution of the disease. In contrast, liquid biopsy can provide unique opportunities for real-time monitoring of disease progression, treatment response and for studying tumor heterogeneity combining the information of DNA that tumors spread in the blood (circulating tumor DNA) with CTCs analysis. In this review, we analyze the technical and biological challenges for isolation and characterization of circulating tumor cells from breast cancer patients. Circulating tumor cell (CTC) enumeration value is included in numerous clinical studies due to the prognostic's role of these cells. Despite this, there are so many questions pending to answer. How to manage lymphocytes background, how to distinguish the CTCs subtypes or how to work with frozen samples, are some of the issues that will discuss in this review. Based on our experience, we try to address these issues and other technical limitations that should be solved to optimize the standardization of protocols, sample extraction procedures, circulating-tumor material isolation (CTCs vs. ctDNA) and the very diverse methodologies employed, aiming to consolidate the use of CTCs in the clinic. Furthermore, we think that new approaches focusing on isolation CTCs in other body fluids such as cerebrospinal or ascitic fluid are necessary to increase the opportunities of circulating tumor cells in the practice clinic as well as to study the promising role of CTC clusters and their prognostic value in metastatic breast cancer. [ABSTRACT FROM AUTHOR]