Disclosures Two disturbing and emerging epidemiologic public health trends in cancer survivors are on a catastrophic collision course set to create a tidal wave of illness bound to flood health systems worldwide. First, the worldwide demographic transition, where high birth and death rates transition to lower birth and death rates as countries continue to develop from pre-industrial to industrialized economic systems, will create an explosion of elderly patients. The second concerning trend is the emerging obesity pandemic. Obesity, a largely preventable multifactorial systemic inflammatory condition associated with a wide variety of illnesses and a marker of suboptimal health, and a major cause of morbidity and mortality, is also on the rise. It is predicted that the illness burden created by an elderly cancer survivor boom will be synergistically inflamed by an alarming pandemic of obese patients. Breast cancer is the most common cancer in females, and breast cancer survivors represent the prototypical population affected by aging and obesity survivor trends. Here, the potential burden of an aging and increasingly obese population on our healthcare system will be highlighted by utilizing trends in breast cancer survivors and United States (US) epidemiologic trends. According to the recently released US Census Bureau’s population estimates, older people are projected to outnumber children for the first time in US history . Virtually every country in the world is experiencing growth in the number and proportion of older persons in their population . Consequently, the largest growth in cancer survivors has been projected to occur in the age 65 and older group  (Figure 1). Obesity rates worldwide have nearly tripled since 1975  and by 2030 an estimated 38% of the world’s adult population will be overweight and another 20% will be obese . In the US, it is projected that 85% of adults will be overweight or obese by 2030 . In conjunction with the demographic transition, the prevalence of obesity has markedly increased in the elderly as well . Unsurprisingly, more than 630,000 people in the US were diagnosed with a cancer linked with being overweight or obese in 2014 and the rates of 12 out of 13 obesity-related cancers, including breast cancer, have risen 7% from 2005 to 2014 . Sadly, obesity has now overtaken tobacco use as the leading cause of preventable death in the US . Of dire concern, many Americans do not understand the health risk of obesity and, shockingly, half of Americans are unaware of the link between obesity and cancer . Figure 1. Estimated cancer prevalence by age in the U.S population from 1975 to 2040. (From Bluethmann SM et al.) × Older breast cancer patients are particularly vulnerable to the harmful consequences of obesity. Not only is obesity associated with increased postmenopausal breast cancer risk, but also obesity is associated with shorter time to disease recurrence and greater mortality for postmenopausal breast cancer patients . For example, in a multiethnic cohort study, obesity was associated with higher all-cause and breast cancer-specific mortality irrespective of ethnicity in American women older than 50 years . Obese breast cancer survivors are at further risk of top morbid conditions including, but not limited to, cardiovascular disease, cerebrovascular disease, hypertension, hyperlipidemia, musculoskeletal disorders, and type 2 diabetes mellitus. Furthermore, obese patients are at increased risk of depression, anxiety, and decreased quality of life. Therefore, increasing obesity rates are predicted to lead to greater rates of associated illnesses and worse cancer outcomes in an increasingly elderly population who, by pre-existing probability, already possess increased comorbidities compared with younger patients. To make things worse, clinical trial data is limited in older adults as they are underrepresented in clinical trials . As a consequential example, NCCN guidelines state that “There are limited data to make chemotherapy recommendations for those 70 years of age” . Therefore, clinicians may have unclear evidenced-based guidance on an increasingly elderly population. Elderly breast cancer patients may be vulnerable to increased toxicity, late effects of standard treatment, and precipitation of an early frailty phenotype. So, in addition to the combination of an older, obese, and therefore increasingly ill, baseline population, breast cancer survivors could incur a multiplicity of negative effects of standard treatments. We seem to be fighting an uphill battle, since weight loss in older adults is difficult to achieve compared with younger adults. There is some evidence that successful weight loss is possible in adults 65 years and older; however, weight loss trials have reported losses of lean body mass and bone mineral density, in addition to fat mass . These negative outcomes may discourage many physicians from advising weight loss to their obese older patients. In addition to physicians being unprepared for the aging obese breast cancer survivor population, health care systems are also unprepared and already overburdened. Medicare, which provides healthcare for the elderly in the US, has already seen increased spending by both insurers and beneficiaries. Breast cancer, along with colon, lung, and prostate cancer, already accounts for half of all expenditures  and breast cancer is on the rise. Currently, the per capita spending on obesity-attributable conditions is greater for Medicare recipients than for younger age groups  and as obesity rates continue to increase, so will per capita spending. Currently, the Medicare budget is overwhelmed by our current demographics and a shift towards an increasing elderly and obese population, and hence an increased burden of illness, will not only exhaust funding but potentially precipitate an implosion of the system. A tsunami of elderly and obese breast cancer patients with increased comorbidities and worse overall prognoses will slam into the US and we are inadequately prepared. Given the lack of public education, insufficient clinical trial data compounded with inadequate weight loss interventions in an era of an increasingly strained Medicare budget, seems like a losing battle. These trends in breast cancer survivors not only represent the archetypal example for many other cancer subtypes, but also may herald a potential seismic effect on outcomes for other medical illnesses including cardiovascular disease, cerebrovascular disease, diabetes, etc. These demographic changes are foreseeable and we are afforded the opportunity to adopt a proactive approach to align policies to the evolving needs of an aging and increasingly obese breast cancer survivor population. An aging survivor population may not be preventable, but obesity is largely preventable. The general public should be educated on preventing obesity though lifestyle changes and recognizing obesity as a serious medical condition with significant associated health risks. Further, as a treatment strategy, we should increase enrollment of elderly and obese patients in clinical trials. Finally, more research is needed in weight loss interventions in elderly cancer patients. If we want to stand a chance against the burden of the aging obese population, all parties including medical societies, government agencies, insurance companies, patient groups, media outlets, health care and education policymakers need to align and make a serious commitment to formulate a comprehensive treatment and prevention strategy to address this potentially catastrophic public health threat.