Obesity: the scale of the problem

Obesity is defined as an excess accumulation of adipose tissue and occurs when energetic intake exceeds energy expenditure. The WHO specifically defines obesity as BMI >30 kg/m², with BMI 25≤BMI<30 kg/m², categorised as overweight⁽⁸⁾. Storing excess energy served a valuable evolutionary purpose to allow our ancestors to store energy in times of nutritional deprivation. However, obesity is now a pandemic health concern in both developed and developing countries, with over 600 million adults worldwide estimated to be obese⁽⁹⁾. In the UK, 27 % of British women are obese and this figure is predicted to increase to 43 % by 2030^(10, Reference Wang, McPherson and Marsh¹¹⁾. The links with type 2 diabetes and CVD have long been established, but it has also become increasingly clear that there is a substantial link between obesity and an increased frequency of a number of cancers⁽Reference Renehan, Tyson and Egger¹²⁾. The International Agency for Research on Cancer has identified thirteen obesity-related cancers, which include oesophageal adenocarcinoma, stomach, colorectal, liver, gallbladder, pancreas, post-menopausal breast, endometrium, ovary, renal cell, thyroid, meningioma and multiple myeloma⁽Reference Lauby-Secretan, Scoccianti and Loomis¹³⁾. Therefore, for these types of cancer, the proportion of patients with obesity is likely to be significant. These associations are further worrying given the increasing prevalence of childhood obesity, potentially increasing the incidence of cancer as these obese children reach adulthood⁽Reference Jeffreys, Smith and Martin¹⁴⁾.

Obesity and risk of breast cancer

The World Cancer Research Fund (WCRF) review has classified the evidence that body fatness increases the relative risk of post-menopausal breast cancer as convincing⁽⁵⁾. This risk is of the order of 12 % higher for women who are overweight (BMI 25–29·9 kg/m²) and 16 % higher who are obese (BMI ≥30 kg/m²), compared with women of healthy body mass (BMI 20–24·9 kg/m²)⁽Reference Cheraghi, Poorolajal and Hashem¹⁵⁾. For every 5 kg/m² increase in BMI, there is a 12 % increased relative risk of post-menopausal breast cancer⁽Reference Renehan, Tyson and Egger¹²⁾. Obese post-menopausal women have an increased risk of hormone receptor-positive breast cancer compared with women of healthy BMI; however, obesity is not associated with an increased risk of hormone receptor-negative breast cancer in post-menopausal women⁽Reference Munsell, Sprague and Berry¹⁶⁾.

Post-menopausal hormone replacement therapy may modify the relationship between obesity and post-menopausal breast cancer. The Nurses’ Health Study found that BMI and adult weight gain were associated with 60 % to 2-fold increased relative risk, respectively, of post-menopausal breast cancer among women who had never used hormone replacement therapy, whereas there was an attenuation of this relationship among women who used hormones⁽Reference Huang, Hankinson and Colditz¹⁷⁾. In terms of women who used hormone therapy, results from the Women's Health Initiative showed an increased risk of post-menopausal breast cancer for oestrogen–progestogen preparations compared with oestrogen alone⁽Reference Morimoto, White and Chen¹⁸⁾. The attenuation of the risk seen in women who use hormone replacement therapy may be due to the fact that circulating oestrogen levels are elevated among women using hormone replacement therapy, minimising the impact of the adipose tissue oestrogen production, which is the primary source of oestrogen production via the aromatase enzyme in post-menopausal women.

In contrast, studies indicate that obesity does not increase the risk of developing premenopausal breast cancer with some meta-analyses even suggesting that the risk is slightly lower in pre-menopausal women who are overweight and obese compared with healthy weight individuals^(5, Reference Renehan, Tyson and Egger^12, Reference Cheraghi, Poorolajal and Hashem^15, Reference Chen, Liu and Zhou¹⁹⁾. However, weight gain during adulthood is associated with a significant increased risk of post-menopausal breast cancer⁽Reference Keum, Greenwood and Lee²⁰⁾.

Mechanisms of cancer development in obesity

The molecular mechanisms promoting cancer development in obesity are not fully understood; however, it is clear that a number of different biological pathways are involved⁽Reference Khandekar, Cohen and Spiegelman²¹⁾. In addition to storing excess energy in the form of lipid, adipose tissue has an active role in endocrine signalling to the rest of the body. Increased adipose tissue is associated directly with increased levels of many circulating hormones, including insulin, insulin-like growth factors and sex hormones, creating an environment that encourages carcinogenesis⁽Reference De Pergola and Silvestris²²⁾. Abdominal fatness is also associated with insulin resistance, further increasing the pancreatic production of insulin⁽Reference Gunter, Hoover and Yu²³⁾. In addition, extensive data suggest that adipose tissue secretes specific molecules into the bloodstream, which signal to other organs to coordinate responses to an altered metabolic state⁽Reference Khandekar, Cohen and Spiegelman²¹⁾. One example is leptin, an adipocyte-derived hormone that is the central mediator of a feedback loop that regulates appetite and energy homeostasis⁽Reference Jardé, Perrier and Vasson²⁴⁾. There is an up-regulation of the leptin receptor in breast cancer, and leptin also stimulates the expression and activity of aromatase and the transactivation of the oestrogen receptor (ER) in breast cancer cells, both of which stimulate tumour growth⁽Reference Jardé, Perrier and Vasson^24–Reference Catalano, Mauro and Marsico²⁶⁾. Several studies indicate an anti-tumour effect of adiponectin⁽Reference Jardé, Perrier and Vasson²⁴⁾. Adiponectin levels are reduced in obesity and inversely associated with breast cancer risk in post-menopausal women⁽Reference Ruan, Zarnowski and Cushman²⁷⁾.

More recently, obesity has become recognised as a chronic pro-inflammatory state.

Cytokines secreted by adipose tissue can activate macrophages, and in obese individuals, adipose tissue becomes infiltrated with macrophages⁽Reference Weisberg, McCann and Desai^28, Reference Xu, Barnes and Yang²⁹⁾. It has been demonstrated that tumour-associated macrophages have a key role in the tumour micro-environment. Increased macrophage chemoattractant protein 1 in breast tumour extracts is an early predictor of early relapse and metastasis⁽Reference Qian, Li and Zhang^30, Reference Ueno, Toi and Saji³¹⁾. Proliferating macrophages in breast tumours are also associated with a high tumour grade and poor prognosis⁽Reference Campbell, Tonlaar and Garwood³²⁾. Adipocytes are also able to produce pro-inflammatory factors such as TNF-α, C-reactive protein and IL-6, and higher serum levels of these cytokines are seen in obese than lean individuals suggesting that obesity has a systemic as well as local pro-inflammatory effect⁽Reference De Pergola and Silvestris²²⁾. It has been proposed that carcinogenesis is promoted by the activation of the inflammatory cascade⁽Reference Calle and Kaaks³³⁾ (Fig. 1).

Fig. 1. (Colour online) Inflammatory signalling in obesity. Circulating leptin produced by adipocytes can bind both to the leptin receptor and the IL-6 receptor. This leads to the activation of the JAK-signal transducer and activation of the transcription (STAT) signalling pathway through STAT3. STAT3 functions as an oncogenic transcription factor. Inflammatory cells in the adipose tissue produce IL-6 and TNF-α. IL-6 promotes proliferation and metastasis by activating the JAK–STAT pathway. TNF-α binds to the TNF receptor, activating NF-κB through the degradation of IκB. NF-κB is free to translocate to the nucleus, where it inhibits apoptosis and promotes proliferation and metastasis. Similarly, macrophages are also able to activate the IL-6 and TNF receptors⁽Reference Khandekar, Cohen and Spiegelman²¹⁾.

Clearer elucidation of the complex molecular mechanisms that underlie tumour development in obesity is required and may unlock the potential for therapeutic interventions, notably in the modulation of inflammatory pathways as chemoprevention.

Obesity and breast cancer outcomes

Several published meta-analyses indicate that obesity is a prognostic factor for poorer outcomes after a diagnosis of breast cancer⁽Reference Chan, Vieira and Aune^6, Reference Ewertz, Jensen and Gunnarsdottir^34, Reference Protani, Coory and Martin³⁵⁾. In the largest of these, Chan et al. reported a meta-analysis of eighty-two clinical studies including 213 075 breast cancer survivors. A pre-diagnosis BMI ≥30 kg/m² was associated with a total mortality of relative risk 1·41 (95 % CI 1·29, 1·53) compared with a reference group of healthy weight patients (BMI 20–24·9); the relative risk for BMI 25–29·9 was also significantly raised at 1·07 (95 % CI 1·02, 1·12)⁽Reference Chan, Vieira and Aune⁶⁾. Each additional 5 kg/m² BMI before diagnosis was associated with a 17 % increase in total mortality and a 18 % increase in breast cancer mortality (11 % increase in total mortality and 14 % increase in breast cancer mortality at <12 months from diagnosis and 8 and 29 %, respectively, at >12 months from diagnosis)⁽Reference Chan, Vieira and Aune⁶⁾. The long-term effects of obesity at diagnosis were highlighted by a study of just under 19 000 Danish women treated for early-stage breast cancer between 1977 and 2006, in which Ewertz et al. found that the risk of distant metastases separated after approximately 3 years, showing a trend of increasing risk with increasing BMI. At 10 years, the incidences were 20·1 % for patients with BMI <25 kg/m², 22·4 % for patients with BMI 25–29 kg/m² and 24·3 % for patients with BMI ≥30 kg/m². At 30 years, the cumulative risks of dying of breast cancer were 46·4 % for patients with BMI <25 kg/m², 53·4 % for patients with BMI 25–29 kg/m² and 57·2 % for patients with BMI ≥30 kg/m²⁽Reference Ewertz, Jensen and Gunnarsdottir³⁴⁾.

Despite the significant quantity of generally consistent data linking obesity at diagnosis of early breast cancer to poorer overall mortality and breast cancer-specific mortality, the 2014 WCRF continuous update project on breast cancer survivors report categorised the level of evidence as limited on the basis it was not clear to what extent individual studies have fully adjusted for potential confounders such as the tumour type, type of treatment, amount of treatment received and the dissemination of the disease⁽⁷⁾ (Table 2).

Table 2. World Cancer Research Fund continuous update project on diet, nutrition, physical activity and breast cancer survivors, 2014; summary of panel judgements⁽⁷⁾*

* This material has been reproduced from the World Cancer Research Fund International/Americal Institute for cancer research continuous update project report: diet, nutrition, physical activity and breast cancer surivivors (2014). Available at www.wcrf.org/int/research-we-fund/continous-update-project-reports/breast-cancer-survivors.

Despite the absence of an association between obesity and the risk of developing breast cancer in pre-menopausal women, there is evidence that obesity is significantly associated with poor outcomes in pre-menopausal breast cancer patients. The UK Prospective Study of Sporadic and Hereditary breast cancer in young women, a cohort study of almost 3000 women aged 40 years and under at diagnosis found that obese patients have significantly lower 8-year overall survival than healthy weight patients (58·6 v. 73·3 %, P < 0·001)⁽Reference Copson, Cutress and Maishman³⁶⁾. Multivariable analyses adjusting for tumour grade, size, nodal and human epidermal growth factor receptor 2 status indicated that obesity was a significant independent predictor of overall survival (hazard ratio 1·65, P < 001) and distant disease-free survival (hazard ratio 1·44). The Chan et al. meta-analysis confirmed that the impact of obesity at diagnosis is greater on pre-menopausal women than post-menopausal women with obesity associated with summary relative risks of 1·75 (95 % CI 1·26, 2·41) for pre-menopausal and 1·34 (95 % CI 1·18, 1·53) for post-menopausal breast cancer⁽Reference Chan, Vieira and Aune⁶⁾.

Presentation and pathology

Compared with those with BMI <25 kg/m², patients with BMI ≥30 kg/m² tend to have larger tumours and more positive axillary lymph nodes involvement⁽Reference Ewertz, Jensen and Gunnarsdottir^34, Reference Majed, Moreau and Senouci³⁷⁾. These unfavourable pathological features could be explained by a delayed presentation in this group of patients: a larger body habitus may result in breast lumps being less palpable or obvious. More recently, the UK Prospective study of Sporadic and Hereditary breast cancer in young women reported on young breast cancer patients who were below screening age and therefore all presented symptomatically. This study showed that again, in obese and overweight patients, median tumour size was significantly higher and there were more node-positive tumours than in healthy weight patients⁽Reference Copson, Cutress and Maishman³⁶⁾. In these cohort studies, multivariate analysis demonstrated that obesity retained an independent effect on prognosis on adjustment for disease stage.

Additionally, a number of studies have also reported increased frequency of grade 3 tumours in obese breast cancer patients, compared with those with a healthy weight⁽Reference Ewertz, Jensen and Gunnarsdottir^34, Reference Majed, Moreau and Senouci³⁷⁾, and increased frequency of ER-negative and oestrogen/progesterone/human epidermal growth factor receptor 2 (triple) negative tumours has also been demonstrated⁽Reference Copson, Cutress and Maishman³⁶⁾. These features are all well-established biomarkers of aggressive behaviour in early breast cancer and these associations suggest that obesity may influence the intrinsic biology of breast tumours, perhaps by affecting the tumour micro-environment. Studies which have adjusted for grade and human epidermal growth factor receptor 2 status suggest that obesity exerts an additional effect beyond these prognostic factors⁽Reference Ewertz, Jensen and Gunnarsdottir^34, Reference Copson, Cutress and Maishman^36, Reference Majed, Moreau and Senouci³⁷⁾. Data on the effect of obesity in ER-positive and ER-negative tumours are more conflicting. Although some reports have indicated an equivalent effect of obesity on the outcome of ER-positive and ER-negative tumours⁽Reference Niraula, Ocana and Ennis³⁸⁾, more recent studies have reported a stronger effect of obesity on the outcome of women with ER-positive breast tumours than ER-negative tumours⁽Reference Copson, Cutress and Maishman^36, Reference Pan and Gray^39, Reference Sparano, Wang and Zhao⁴⁰⁾. Pan et al. demonstrated a breast cancer mortality-adjusted relative risk of 1·34 (95 % CI 1·22, 1·47) associated with obesity in peri/pre-menopausal ER-positive patients but no association between BMI and breast cancer mortality in ER-negative patients⁽Reference Pan and Gray^39, Reference Sparano, Wang and Zhao⁴⁰⁾. However, it should be noted that many data sets contained relatively small numbers of ER-negative patients and analyses may have been underpowered in this patient group.

Local treatment issues

Systemic treatment issues

Cytotoxic therapy

In adult patients with cancer, chemotherapy dosing has traditionally been based on a patient's estimated body surface area (BSA), calculated from their height and weight⁽Reference DuBois and DuBois⁵⁴⁾. Chemotherapy is given either before (neoadjuvant) or after (adjuvant) surgery to selected patients with early breast cancer in order to reduce the risk of future metastatic disease. It is well established that administering adjuvant chemotherapy on time and at the optimal dose is vital to achieve maximal risk reduction with the classic publication by Belladonna indicating that a chemotherapy dose intensity <85 % of the intended dose intensity was equivalent to not giving any chemotherapy at all⁽Reference Bonadonna, Moliterni and Zambetti⁵⁵⁾. However, concerns about the potential toxicity of cytotoxic doses associated with high calculated BSA have led to many oncologists routinely capping chemotherapy doses at a maximum BSA of 2·0 or using either ideal body weight or adjusted ideal body weight to calculate drug doses. Reviews of routine practice indicate that up to 40 % of obese patients receive limited doses that are not based on actual body weight and it has been postulated that this use of sub-optimal chemotherapy doses results in a reduced therapeutic effect, which could potentially explain the observed adverse prognosis of obese patients⁽Reference Lyman, Dale and Crawford^56–Reference Chan, Vieira and Aune⁶⁰⁾.

An expert panel review of the literature found no evidence that short- or long-term toxicity is increased in obese patients receiving full weight-based chemotherapy doses and the resultant American Society of Clinical Oncology clinical practice guideline recommends that full weight-based cytotoxic chemotherapy doses be used to treat obese patients with cancer⁽Reference Griggs, Mangu and Anderson⁶¹⁾ (Table 3). However, it should be noted that the data presented were taken largely from clinical trial patients and it is possible that patients in trials have been selected for a certain level of medical fitness; therefore, these data may not fully represent the real-world situation. In addition, the data collected largely looked only at haematological toxicity criteria. The need for more research in this area was therefore highlighted by American Society of Clinical Oncology⁽Reference Griggs, Mangu and Anderson⁶¹⁾. A subsequent meta-analysis of 9134 chemotherapy patients treated on the basis of actual body weight found similar or lower rates of toxic effects compared with normal-weight patients⁽Reference Hourdequin, Schpero and McKenna⁶²⁾. However, a more recent study of data from 3023 patients with breast cancer published after this did demonstrate an increase in significant toxicity in obese patients given dose-intense anthracycline and taxane chemotherapy regimens dosed according to actual body weight⁽Reference Furlanetto, Eiermann and Marme⁶³⁾.

Table 3. Summary of American Society of Clinical Oncologists panel recommendations for treatment of obese patients⁽Reference Field, Kosmider and Jefford⁵⁹⁾

The consequences of a high proportion of obese patients being treated with reduced doses are that survival advantages are lost and outcomes are potentially similar to those of the untreated cohorts. This is seen in trials (of different cancer types including breast) where participants received reduced doses of adjuvant chemotherapy, and where the adjuvant chemotherapy is known to improve survival⁽Reference Wildiers and Reiser^64, Reference Budman, Berry and Cirrincione⁶⁵⁾. It may also be the case that the observed adverse prognosis of obese patients may be the result of the sub-therapeutic chemotherapy doses and reduced therapeutic effect rather than obesity as a stand-alone factor⁽Reference Hunter, Navo and Thaker⁶⁶⁾.

Studies of pathological response rates in the neoadjuvant treatment setting offer to provide a further insight into the effect of obesity on the effectiveness of systemic therapies; however, currently the available data are conflicting. Although a number of studies have reported higher BMI associated with poorer pathological complete response rates and inferior overall survival⁽Reference Litton, Gonzalez-Angulo and Warneke^67–Reference Fontanella, Lederer and Gade⁶⁹⁾, other studies have not found this association⁽Reference Farr, Stolz and Baumann⁷⁰⁾. This may also be explained by variations in chemotherapy prescribing habits as Farr et al.⁽Reference Farr, Stolz and Baumann⁷⁰⁾ confirmed that all obese patients analysed had received full uncapped doses of anthracycline–taxane-based chemotherapy whilst prescribing data were not available in all the other publications.

Weight changes during treatment for breast cancer

Weight gain during chemotherapy is a common feature of treatment with contemporary regimens of 4–6 months of anthracycline and taxane chemotherapy, which are the standard regimens for early breast cancer. European, American and Asian studies report that 30–50 % of women gain more than 5 % of body weight, with a mean weight change of 2–3 kg in the first year after diagnosis⁽Reference Makari-Judson, Judson and Mertens^77–Reference Renehan, Harvie and Cutress⁸⁸⁾. There is a persistence of weight gain when measured at 3 and 6 years after diagnosis⁽Reference Lankester, Phillips and Lawton^78, Reference Harvie, Campbell and Baildam⁸⁵⁾. Weight is gained both during and after the chemotherapy period⁽Reference Freedman, Aziz and Albanes^83, Reference Harvie, Campbell and Baildam⁸⁵⁾. The cause of weight gain due to chemotherapy is usually multifactorial, with use of steroids, change in eating patterns, reduction in physical activity due to fatigue, oedema secondary to taxane chemotherapy and hormonal changes all playing a role. The greatest weight gain is observed in women who are premenopausal, stop smoking after the diagnosis, have a healthy weight at diagnosis or experience a chemotherapy-induced menopause⁽Reference Makari-Judson, Judson and Mertens^77, Reference Freedman, Aziz and Albanes^83, Reference Sedjo, Byers and Ganz^86, Reference Goodwin, Ennis and Pritchard⁸⁷⁾. Studies indicate changes in body composition with gain of fat mass and loss of muscle as well as alterations in fluid compartments⁽Reference Renehan, Harvie and Cutress⁸⁸⁾.

The consequences of chemotherapy-related weight gain was addressed by Playdon et al. in their meta-analysis of 23 832 cancer cases where they found that, compared with women who maintained their weight, those women with a >10 % weight gain after diagnosis had increased overall mortality (hazard ratio 1·23; 95 % CI 1·09, 1·39, P < 0·001); breast cancer-specific mortality was increased but not to a statistically significant level (hazard ratio 1·17; 95 % CI 1·00, 1·38, P = 0·05)⁽Reference Playdon, Bracken and Sanft⁸⁹⁾. No association between weight gain and recurrence was identified. In contrast, in a pooled analysis of 6596 women with ER-positive tumours, more than 10 % weight gain was associated with an increased risk of late recurrence, defined as more than 5 years after diagnosis⁽Reference Nechuta, Chen and Cai⁹⁰⁾.

Limitations of using BMI

BMI is a simple surrogate marker of obesity, but it is not a reliable measure of body fat for individuals as it cannot distinguish lean mass from fat mass, or characterise body fat distribution. Body fat is generally distributed viscerally, subcutaneously and internally (most in the liver), and the body fat distribution pattern can differ significantly between individuals with the same BMI. Similarly, patients with the same BSA may have wide variations in the distribution of adipose tissue and skeletal muscle; thus, BSA fails to accurately reflect drug pharmacodynamics and pharmacokinetic variability in obese patients. In a large analysis of 1206 cancer patients, Sparreboom et al. showed drug-specific interactions between BMI and the pharmacokinetic clearance of cytotoxic drugs including doxorubicin, which is commonly used in the treatment of early breast cancer⁽Reference Sparreboom, Wolff and Mathijssen⁹¹⁾.

Very few studies have looked at the effect of body composition patterns on chemotherapy tolerance because the gold standard ‘four-compartment model’ measurement of body composition requires complex procedures not routinely available in the clinical environment. Two small series using limited body composition data derived from comprised tomography images indicate that sarcopaenia (low muscle mass) is associated with increased chemotherapy toxicity, regardless of overall BMI⁽Reference Prado, Baracos and McCargar^92, Reference Prado, Antoun and Sawyer⁹³⁾. Sarcopaenia may result in a relatively higher chemotherapy dose as lean body mass is a predictor of volume of distribution for some drugs⁽Reference Morgan and Bray⁹⁴⁾. Del Fabbro et al. reported a higher pathological complete response rate to neoadjuvant chemotherapy for breast cancer in healthy BMI patients with sarcopaenia⁽Reference Del Fabbro, Parsons and Warneke⁹⁵⁾.

In a larger study, Iwase et al. retrospectively analysed 172 advanced breast cancer patients who underwent surgery after neoadjvuant chemotherapy⁽Reference Iwase, Sangai and Nagashima⁹⁶⁾. Body composition parameters including abdominal circumference, subcutaneous fat area, visceral fat area and skeletal muscle area were calculated using comprised tomography volume-analysing software. Distant disease-free survival was significantly worse in the high visceral fat area group than in the lower visceral fat area group. Furthermore, in the high visceral fat area group, post-menopausal patients had significantly shorter distant disease-free survival than premenopausal patients⁽Reference Del Fabbro, Parsons and Warneke⁹⁵⁾. The importance of visceral fat may be explained by the fact that it appears to be more hormonally active than other types of body fat; this appears to promote inflammation, insulin resistance and increases in leptin and adiponectin.

Further research is clearly required to fully assess the interactions between body composition and chemotherapy toxicity and effectiveness⁽Reference James, Wootton and Jackson⁹⁷⁾. Techniques such as dual-energy X-ray absorptiometry, bioelectrical impedance, computerised tomography scan software and MRI analysis provide a clearer picture of body composition and may have a role in the management and treatment planning of obese patients in the future⁽Reference Renehan, Harvie and Cutress⁸⁸⁾. However, clearly the risk-benefits and cost-effectiveness of such approaches will need to be addressed as currently it is not a routine practice for all early breast cancer patients to undergo cross-sectional imaging for staging purposes.

Health behaviour

Finally, it cannot be excluded that obesity or body fatness are surrogate markers for other health behaviours in addition to dietary ones. The WCRF continuous update project on diet, nutrition, physical activity and breast cancer survivors additionally investigated the impact of physical activity both before and after a diagnosis of breast cancer on long-term survival. They concluded that there was limited but consistent evidence that physical activity prior to diagnosis was associated with a reduction in both all-cause and breast cancer mortality⁽⁷⁾. The same conclusion was reached regarding physical activity after breast cancer diagnosis. Similar results were reported by the After Breast Cancer Pooling Project, which reported a 27 % significant decreased risk of mortality and a 25 % reduction in breast cancer mortality associated with engagement in at least 10 metabolic equivalent per task hours per week compared with <10 metabolic equivalent per task hours per week⁽Reference Beasley, Kwan and Chen⁹⁸⁾. The WCRF has therefore concluded that there is sufficient evidence to recommend that early breast cancer patients follow the WCRF cancer prevention recommendations, which include being physically active in addition to eating a healthy diet and maintaining a healthy weight. However, more evidence is needed in order to make specific recommendations on lifestyle modifications for breast cancer survivors. Prospective studies to evaluate whether weight loss and lifestyle interventions will improve breast cancer outcomes are now in progress.