Body mass index and breast size in women: same or different genes?

The effect of female breast surface area on skin stiffness and tactile sensitivity at rest and following exercise in the heat

Female development includes significant morphological changes across the breast. Yet, whether differences in breast surface area (BrSA) modify breast skin stiffness and tactile sensitivity at rest and after exercise in the heat remain unclear. We investigated the relationship between BrSA and skin stiffness and tactile sensitivity in 20 young to middle-aged women (27 ± 8 years of age) of varying breast sizes (BrSA range: 147-502 cm2) at rest and after a submaximal run in a warm climatic chamber (32 C ${\mathrm{C}}$  ± 0 . 6 C ; ${\mathrm{0}}{\mathrm{.6C;}}$ 53% ± 1.7% relative humidity). Skin stiffness above and below the nipple and tactile sensitivity from the nipple down were measured. Associations between BrSA and both skin stiffness and tactile sensitivity at rest were determined via correlation analyses. Effects of exercise and test site were assessed by a two-way ANOVA. Skin stiffness was positively correlated with BrSA 3 cm above the areola edge (r = 0.61, P = 0.005) and at the superior areola border (r = 0.54, P = 0.016), but not below the nipple (P > 0.05). The area 3 cm below the areola was also significantly stiffer than all other test sites (P < 0.043). Tactile sensitivity did not vary with BrSA (P > 0.09), but it varied across the breast (i.e., the area 3 cm below the areola was more sensitive than the inferior areola edge; P = 0.018). Skin stiffness and tactile sensitivity across the breast decreased after exercise by ∼37% (P < 0.001) and ∼45% (P = 0.008), respectively. These findings expand our fundamental understanding of the mechanosensory properties of the female breast, and they could help to inform sportswear innovation to better meet the support needs of women of different breast sizes at rest and following exercise.

The effect of female breast surface area on heat-activated sweat gland density and output

Female development includes significant morphological changes across the breast. Yet, whether differences in breast surface area (BrSA) modify sweat gland density and output remains unclear. The present study investigated the relationship between BrSA and sweat gland density and output in 22 young to middle-aged women (28± $\ \pm \ $ 10 years) of varying breast sizes (BrSA range: 147-561 cm2) during a submaximal run in a warm environment (32 ± $ \pm \ $ 0.6°C; 53 ± $ \pm \ $ 1.7% relative humidity). Local sweat gland density and local sweat rate (LSR) above and below the nipple and at the bra triangle were measured. Expired gases were monitored for the estimation of evaporative requirements for heat balance (Ereq, in W/m2). Associations between BrSA and (i) sweat gland density; (ii) LSR; and (iii) sweat output per gland for the breast sites were determined via correlation and regression analyses. Our results indicated that breast sweat gland density decreased linearly as BrSA increased (r = -0.76, P < 0.001), whereas sweat output per gland remained constant irrespective of BrSA (r = 0.29, P = 0.28). This resulted in LSR decreasing linearly as BrSA increased (r = -0.62, P = 0.01). Compared to the bra triangle, the breast had a 64% lower sweat gland density (P < 0.001), 83% lower LSR (P < 0.001) and 53% lower output per gland (P < 0.001). BrSA (R2 = 0.33, P = 0.015) explained a greater proportion of variance in LSR than Ereq (in W/m2) (R2 = 0.07, P = 0.538). These novel findings extend the known relationship between body morphology and sweat gland density and LSR, to the female breast. This knowledge could innovate user-centred design of sports bras by accommodating breast size-specific needs for sweat management, skin wetness perception and comfort.

Female thermal sensitivity and behaviour across the lifespan: A unique journey

Women are a group of individuals that undergo unique anatomical, physiological and hormonal changes across the lifespan. For example, consider the impact of the menstrual cycle, pregnancy and menopause, all of which are accompanied by both short- and long-term effects on female body morphology (e.g., changes in breast size) and temperature regulation, heat tolerance, thermal sensitivity and comfort. However, empirical evidence on how skin thermal and wetness sensitivity might change across the lifespan of women, and the implications that this has for female-specific thermal behaviours, continues to be lacking. This paper is based on a symposium presentation given at Physiology 2023 in Harrogate, UK. It aims to review new evidence on anatomical and physiological mechanisms underpinning differences in skin thermal and wetness sensitivity amongst women varying in breast size and age, in addition to their role in driving female thermal behaviours. It is hoped that this brief overview will stimulate the development of testable hypotheses to increase our understanding of the behavioural thermal physiology of women across the lifespan and at a time of climate change.

Look how far we have come: BREAST cancer detection education on the international stage

The development of screening mammography over 30 years has remarkedly reduced breast cancer-associated mortality by 20%-30% through detection of small cancer lesions at early stages. Yet breast screening programmes may function differently in each nation depending on the incidence rate, national legislation, local health infrastructure and training opportunities including feedback on performance. Mammography has been the frontline breast cancer screening tool for several decades; however, it is estimated that there are 15% to 35% of cancers missed on screening which are owing to perceptual and decision-making errors by radiologists and other readers. Furthermore, mammography screening is not available in all countries and the increased speed in the number of new breast cancer cases among less developed countries exceeds that of the developed world in recent decades. Studies conducted through the BreastScreen Reader Assessment Strategy (BREAST) training tools for breast screening readers have documented benchmarking and significant variation in diagnostic performances in screening mammogram test sets in different countries. The performance of the radiologists from less well-established breast screening countries such as China, Mongolia and Vietnam were significant lower in detecting early-stage cancers than radiologists from developed countries such as Australia, USA, Singapore, Italy. Differences in breast features and cancer presentations, discrepancies in the level of experiences in reading screening mammograms, the availability of high-quality national breast screening program and breast image interpretation training courses between developed and less developed countries are likely to have impact on the variation of readers' performances. Hence dedicated education training programs with the ability to tailor to different reader cohorts and different population presentations are suggested to ameliorate challenges in exposure to a range of cancer cases and improve the interpretation skills of local radiologists. Findings from this review provide a good understanding of the radiologist' performances and their improvement using the education interventions, primarily the BREAST program, which has been deployed in a large range of developing and developed countries in the last decade. Self-testing and immediate feedback loops have been shown to have important implications for benchmarking and improving the diagnostic accuracy in radiology worldwide for better breast cancer control.

Chest Feminization in Male-to-Female Transgender Patients: A Review of Options

Management of a transgender (TG) woman's gender dysphoria is individualized to address the sources of her distress. This typically involves some combination of psychological therapy, hormone modulation, and surgical intervention. Breast enhancement is the most commonly pursued physical modification in this population. Because hormone manipulation provides disappointing results for most TG women, surgical treatment is frequently required to achieve the goal of a feminine chest. Creating a female breast from natal male chest anatomy poses significant challenges; the sexual dimorphism requires a different approach than that used in cisgender breast augmentation. The options and techniques used continue to evolve as experience in this field grows.

The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis

The possession of permanent, adipose breasts in women is a uniquely human trait that develops during puberty, well in advance of the first pregnancy. The adaptive role and developmental pattern of this breast morphology, unusual among primates, remains an unresolved conundrum. The evolutionary origins of this trait have been the focus of many hypotheses, which variously suggest that breasts are a product of sexual selection or of natural selection due to their putative role in assisting in nursing or as a thermoregulatory organ. Alternative hypotheses assume that permanent breasts are a by-product of other evolutionary changes. We review and evaluate these hypotheses in the light of recent literature on breast morphology, physiology, phylogeny, ontogeny, sex differences, and genetics in order to highlight their strengths and flaws and to propose a coherent perspective and a new hypothesis on the evolutionary origins of perennially enlarged breasts in women. We propose that breasts appeared as early as Homo ergaster, originally as a by-product of other coincident evolutionary processes of adaptive significance. These included an increase in subcutaneous fat tissue (SFT) in response to the demands of thermoregulatory and energy storage, and of the ontogenetic development of the evolving brain. An increase in SFT triggered an increase in oestradiol levels (E2). An increase in meat in the diet of early Homo allowed for further hormonal changes, such as greater dehydroepiandrosterone (DHEA/S) synthesis, which were crucial for brain evolution. DHEA/S is also easily converted to E2 in E2-sensitive body parts, such as breasts and gluteofemoral regions, causing fat accumulation in these regions, enabling the evolution of perennially enlarged breasts. Furthermore, it is also plausible that after enlarged breasts appeared, they were co-opted for other functions, such as attracting mates and indicating biological condition. Finally, we argue that the multifold adaptive benefits of SFT increase and hormonal changes outweighed the possible costs of perennially enlarged breasts, enabling their further development.

Relationship of breast volume, obesity and central obesity with different prognostic factors of breast cancer

The objective of this study was to investigate whether the BC tumor biology in women with larger breast volume, in obese women and especially in women with central adiposity at the moment of diagnosis of BC is more aggressive than in those women without these characteristics. 347 pre- and postmenopausal women with a recent diagnosis of BC were analyzed. In all patients, anthropometric measurements at the time of diagnosis was collected. In 103 of them, the breast volume was measured by the Archimedes method. The Breast volume, BMI, WHR and the menopausal status were related to different well-known pathological prognostic factors for BC. At the time of diagnosis, 35.4% were obese (BMI > 30 kg/m²), 60.2% had a WHR ≥ 0.85, 68.8% were postmenopausal and 44.7% had a breast volume considered "large" (> 600 cc). Between patients with a large breast volume, only a higher prevalence of ER (+) tumors was found (95.3% vs. 77.2%; p = 0.04) compared to those with small breast volumes. The obese BC patients showed significantly higher rates of large tumors (45.5% vs. 40.6%; p = 0.04), axillary invasion (53.6% vs. 38.8%; p = 0.04), undifferentiated tumors (38.2% vs. 23.2%) and unfavorable NPI (p = 0.04) than non-obese women. Those with WHR ≥ 0.85 presented higher postsurgical tumor stages (61.7% vs. 57.8%; p = 0.03), higher axillary invasion (39.9% vs. 36.0%; p = 0.004), more undifferentiated tumors (30.0% vs. 22.3%; p = 0.009), higher lymphovascular infiltration (6.5% vs. 1.6%; p = 0.02), and a higher NPI (3.6 ± 1.8 vs. 3.2 ± 1.8; p = 0.04). No statistically significant differences were found according to menopausal status. We conclude that obesity, but especially central obesity can be associated with a more aggressive tumour phenotype. No relation between breast volume and tumoral prognostic factors was found, except for a higher proportion of ER (+) tumor in women with higher breast volume.

The Effect of Obesity on Operating Room Utilization in Breast Surgery

BACKGROUND

The current obesity epidemic is associated with increased health care costs associated with comorbidities such as diabetes and heart disease as well as postoperative complications. However, the effect of obesity on operating room (OR) utilization, especially in common breast procedures, has not been completely evaluated. Our study is the first to examine the effect of patient obesity on operative time (OPT) for common breast procedures.

METHODS

The American College of Surgeons National Surgical Quality Improvement Project databases for 2010-2018 were searched for this retrospective review. Patients undergoing common breast operations (lumpectomy, lumpectomy with sentinel lymph node biopsy (SLNB) (+/- injection), lumpectomy and axillary lymph node dissection (ALND), simple mastectomy, mastectomy with SLNB (+/- injection), and mastectomy with ALND) were filtered out by Current Procedural Terminology code and divided into three groups based on their body mass index (BMI) and weight. Using the two-sample t-test, OPT for the procedures was compared among the lowest and highest BMI and weight categories. We also used a linear regression t-test to demonstrate that for every unit increase in BMI, there was a corresponding increase in OPT for each procedure.

RESULTS

When the lowest and highest BMI and weight groups were compared, significant differences in OPT (P < 0.0001) were seen for each of the procedures. Numerous factors that could affect the complexity of surgery and thus OR time were identified. The correlation between BMI and weight and OPT remained significant after controlling for these variables. The differences between the highest and lowest BMI groups were most pronounced for higher complexity procedures, such as lumpectomy with ALND and mastectomy with ALND, with average operating times increasing by 18.2 min and 18.6 min, respectively, for patients with a higher BMI.

CONCLUSIONS

Patient BMI and weight significantly affect OPT for common breast procedures. Therefore, patient BMI should be taken into account to improve OR scheduling.

Causal mediation analysis in presence of multiple mediators uncausally related

Mediation analysis aims at disentangling the effects of a treatment on an outcome through alternative causal mechanisms and has become a popular practice in biomedical and social science applications. The causal framework based on counterfactuals is currently the standard approach to mediation, with important methodological advances introduced in the literature in the last decade, especially for simple mediation, that is with one mediator at the time. Among a variety of alternative approaches, Imai et al. showed theoretical results and developed an R package to deal with simple mediation as well as with multiple mediation involving multiple mediators conditionally independent given the treatment and baseline covariates. This approach does not allow to consider the often encountered situation in which an unobserved common cause induces a spurious correlation between the mediators. In this context, which we refer to as mediation with uncausally related mediators, we show that, under appropriate hypothesis, the natural direct and joint indirect effects are non-parametrically identifiable. Moreover, we adopt the quasi-Bayesian algorithm developed by Imai et al. and propose a procedure based on the simulation of counterfactual distributions to estimate not only the direct and joint indirect effects but also the indirect effects through individual mediators. We study the properties of the proposed estimators through simulations. As an illustration, we apply our method on a real data set from a large cohort to assess the effect of hormone replacement treatment on breast cancer risk through three mediators, namely dense mammographic area, nondense area and body mass index.

Stereotypical and Actual Associations of Breast Size with Mating-Relevant Traits

Breast size varies substantially among women and influences perception of the woman by other people with regard to her attractiveness and other characteristics that are important in social contexts, including mating. The theory of sexual selection predicts that physical criteria of partner selection should be markers of the candidate's desirable properties, mainly biological quality. Few studies, however, have examined whether breast size really signals biological quality or its components and whether observers accurately interpret these signals. Our first study encompassed 163 young women and aimed to establish actual correlates of breast size. The aim of the second study was to determine preferences and stereotypes related to breast size: 252-265 women and men evaluated female digital figures varying in, among other characteristics, breast size. Breast size (breast circumference minus chest circumference) was negatively associated with body asymmetry and positively associated with infections of the respiratory system, but did not correlate with infections of the digestive system, openness to casual sex, and testosterone and estradiol level. Women and men perceived breasts in a similar way to each other: the bigger the breasts the higher the reproductive efficiency, lactational efficiency, sexual desire, and promiscuity attributed to the woman. Nevertheless, large breasts were not regarded more attractive than average ones, though small breasts were the least attractive. In addition, big-breasted women were perceived as less faithful and less intelligent than women with average or small breasts. We discuss our results from the perspectives of evolutionary psychology, perceptual biases, and social stereotypes.

Breast firmness is of greater importance for women's attractiveness than breast size

OBJECTIVES

Male preferences are believed to have played a role in the evolution of permanently enlarged breasts in human females. Although breast size and shape are proven to affect women's attractiveness, their relative importance has not been investigated thus far. We aime to address this gap.

METHODS

We prepared two sets of stimuli, each comprising 49 high-quality color images of a topless woman in a three-quarter view that varied in breast size (from 1 to 7) and firmness (from 1 to 7). Set A depicted the glandular ptosis (ie, breast shape being manipulated but the nipple always directed forward), while Set B depicted true ptosis (both breast shape and nipple position being manipulated). Participants (aged 18-45) were assigned to Set A (62 women, 60 men) or Set B (76 women, 52 men). First, each participant indicated the most attractive woman in the set of images. Next, the participant chose the more attractive woman from pairs in which one female deviated from the participant's ideal in breast size and the other in breast firmness.

RESULTS

Both men and women preferred breasts of average or slightly above-average size and high or extreme firmness. Glandular ptosis was as important for attractiveness as breast size, but true ptosis was of much greater importance. Men preferred slightly bigger breasts than women.

CONCLUSIONS

Further attempts to explain evolution of permanent breasts in human females should give greater attention to breast shape than has previously been the case.

The genetic interplay between body mass index, breast size and breast cancer risk: a Mendelian randomization analysis

BACKGROUND

Evidence linking breast size to breast cancer risk has been inconsistent, and its interpretation is often hampered by confounding factors such as body mass index (BMI). Here, we used linkage disequilibrium score regression and two-sample Mendelian randomization (MR) to examine the genetic associations between BMI, breast size and breast cancer risk.

METHODS

Summary-level genotype data from 23andMe, Inc (breast size, n = 33 790), the Breast Cancer Association Consortium (breast cancer risk, n = 228 951) and the Genetic Investigation of ANthropometric Traits (BMI, n = 183 507) were used for our analyses. In assessing causal relationships, four complementary MR techniques [inverse variance weighted (IVW), weighted median, weighted mode and MR-Egger regression] were used to test the robustness of the results.

RESULTS

The genetic correlation (rg) estimated between BMI and breast size was high (rg = 0.50, P = 3.89x10-43). All MR methods provided consistent evidence that higher genetically predicted BMI was associated with larger breast size [odds ratio (ORIVW): 2.06 (1.80-2.35), P = 1.38x10-26] and lower overall breast cancer risk [ORIVW: 0.81 (0.74-0.89), P = 9.44x10-6]. No evidence of a relationship between genetically predicted breast size and breast cancer risk was found except when using the weighted median and weighted mode methods, and only with oestrogen receptor (ER)-negative risk. There was no evidence of reverse causality in any of the analyses conducted (P > 0.050).

CONCLUSION

Our findings indicate a potential positive causal association between BMI and breast size and a potential negative causal association between BMI and breast cancer risk. We found no clear evidence for a direct relationship between breast size and breast cancer risk.

Assessing the genetic correlations between early growth parameters and bone mineral density: A polygenic risk score analysis

OBJECTIVE

The relationships between early growth parameters and bone mineral density (BMD) remain elusive now. In this study, we performed a large scale polygenic risk score (PRS) analysis to evaluate the potential impact of early growth parameters on the variations of BMD.

METHODS

We used 2286 Caucasian subjects as cohort 1 and 3404 Framingham Heart Study (FHS) subjects as cohort 2 in this study. BMD at ulna & radius, hip and spine were measured using dual energy X-ray absorptiometry. BMD values were adjusted for age, sex, height and weight as covariates. Genome-wide single-nucleotide polymorphism (SNP) genotyping of the 2286 Caucasian subjects was performed using Affymetrix Human SNP Array 6.0. The GWAS datasets of early growth parameters were driven from the Early Growth Genetics Consortium, including birth weight (BW), birth head circumference (BHC), childhood body mass index (CBMI), pubertal height growth related indexes and tanner stage. Polygenic Risk Score (PRSice) and linkage disequilibrium (LD) score regression analysis were conducted to assess the genetic correlation between early growth parameters and BMD.

RESULTS

We detected significant genetic correlations in cohort 1, such as total spine BMD vs. CBMI (p value = 1.51 × 10^-4, rg = 0.4525), right ulna and radius BMD vs. CBMI (p value = 1.51 × 10^-4, rg = 0.4399) and total body BMD vs. tanner stage (p value = 7.00 × 10^-4, rg = -0.0721). For cohort 2, significant correlations were observed for total spine BMD vs. height change standard deviation score (SDS) between 8 years and adult (denoted as PGF + PGM) (p value = 3.97 × 10^-4, rg = -0.1425), femoral neck BMD vs. the timing of peak height velocity by looking at the height change SDS between age 14 years and adult (denoted as PTF + PTM) (p value = 7.04 × 10^-4, rg = -0.2185), and total spine BMD vs. PTF + PTM (p value = 6.86 × 10^-4, rg = -0.2180).

CONCLUSION

Our study results suggest that some early growth parameters could affect the variations of BMD.

Breast Development in Transwomen After 1 Year of Cross-Sex Hormone Therapy: Results of a Prospective Multicenter Study

CONTEXT

Breast development is a key feature of feminization and therefore important to transwomen (male-to-female transgender persons). It is not exactly known when breast development starts after initiating cross-sex hormone therapy (CHT) and how much growth may be expected.

OBJECTIVE

To investigate breast development in transwomen during their first year of CHT and whether clinical or laboratory parameters predict breast development.

DESIGN

This study was performed as part of the European Network for the Investigation of Gender Incongruence, which is a prospective multicenter cohort study.

SETTING

Gender clinics in Amsterdam, Ghent, and Florence.

PARTICIPANTS

Transwomen who completed the first year of CHT (n = 229).

INTERVENTION

CHT.

MAIN OUTCOME MEASURES

Breast development in centimeter and cup size.

RESULTS

The median age of the included transwomen was 28 years (range, 18 to 69). Mean breast-chest difference increased to 7.9 ± 3.1 cm after 1 year of CHT, mainly resulting in less than an AAA cup size (48.7%). Main breast development occurred in the first 6 months of therapy. Serum estradiol levels did not predict breast development after 1 year of CHT (first quartile, 3.6 cm [95% confidence interval (CI), 2.7 to 4.5], second quartile, 3.2 cm [95% CI, 2.3 to 4.2], third quartile, 4.4 cm [95% CI, 3.5 to 5.3], and fourth quartile, 3.6 cm [95% CI, 2.7 to 4.5]).

CONCLUSION

This study shows that, after 1 year of CHT, breast development is modest and occurs primarily in the first 6 months. No clinical or laboratory parameters were found that predict breast development.

Determinants of breast size in Asian women

Breast size as a risk factor of breast cancer has been studied extensively with inconclusive results. Here we examined the associations between breast size and breast cancer risk factors in 24,353 Asian women aged 50 to 64 years old enrolled in a nationwide mammography screening project conducted between October 1994 and February 1997. Information on demographic and reproductive factors was obtained via a questionnaire. Breast size was ascertained as bust line measured at study recruitment and total breast area measured from a mammogram. The average bust line and total breast area was 91.2 cm and 102.3 cm², respectively. The two breast measurements were moderately correlated (Spearman correlation coefficient = 0.65). Age, BMI, marital and working status were independently associated with bust line and total breast area. In the multivariable analyses, the most pronounced effects were observed for BMI (24.2 cm difference in bust line and 39.4 cm² in breast area comparing women with BMI ≥30 kg/m² to BMI <20 kg/m²). Ethnicity was a positive predictor for total breast area, but not bust line.

Do women with smaller breasts perform better in long-distance running?

Literature has established that a range of physiological, biomechanical, and training variables influence marathon performance. The influence of anthropometric characteristics has also received attention. However, despite major marathons exceeding 40,000 participants and approximately a third of these runners being female, no data exist on the influence of the breast on running performance. This cross-sectional study aimed to explore the impact of breast mass on marathon finish time. One hundred and sixty-eight of 321 female marathon runners contacted completed an on-line survey focusing on marathon performance during the 2012 London marathon. Participants were categorised as smaller (<500 g, 54%) or larger breasted (>500 g, 46%). Regression analysis identified that 24% of marathon performance variance could be explained by body mass index (BMI), but breast mass improved the model to explain 28% of performance variation. The model determined that for women with 32/34 or 36/38 underband each increase in cup size equates to a performance decrement of 4.6 min or 8.6 min, equivalent to 34.4 min difference between a woman with 36A compared to 36DD breast size. Larger breasted runners had greater BMIs, completed less marathons and had slower marathon finish times (316 ± 48 min) compared to smaller breasted runners (281 ± 51 min). Twenty-five per cent less larger breasted women finished in the fastest quartile. These results suggest that differences in breast mass are an important factor for female athletes and should be considered in future research in this area.

Effect of sports bra type and gait speed on breast discomfort, bra discomfort and perceived breast movement in Chinese women

This study investigated the effect of sports bra type (encapsulation versus compression) and gait speed on perceptions of breast discomfort, bra discomfort and breast movement reported by Chinese women. Visual analogue scales were used to evaluate breast discomfort, bra component discomfort and perceived breast movement of 21 Chinese participants when they wore an encapsulation or a compression sports bra, while static and while exercising at three different gait speeds. Participants perceived less breast discomfort and breast movement when wearing a compression bra compared to an encapsulation bra at a high gait speed, suggesting that compression bras are likely to provide the most effective support for Chinese women. However, significantly higher bra discomfort was perceived in the compression bra compared to the encapsulation bra when static and at the lower gait speed, implying that ways to modify the design of sports bras, particularly the straps, should be investigated to provide adequate and comfortable breast support.

PRACTITIONER SUMMARY

The compression sports bra provided more comfortable support than the encapsulation sports bra for these Chinese women when running on a treadmill. However, these women perceived higher bra discomfort when wearing the compression bra when stationary. Further research is needed to modify the design of sports bras, particularly the straps, to provide adequate and comfortable breast support.

Variants in 6q25.1 Are Associated with Mammographic Density in Malaysian Chinese Women

BACKGROUND

Mammographic density is an established risk factor for breast cancer and has a strong heritable component. Genome-wide association studies (GWAS) for mammographic density conducted in women of European descent have identified several genetic associations, but none of the studies have been tested in Asians. We sought to investigate whether these genetic loci, and loci associated with breast cancer risk and breast size, are associated with mammographic density in an Asian cohort.

METHODS

We conducted genotyping by mass spectrometry in 1,189 women (865 Chinese, 187 Indian, and 137 Malay). Quantitative measurements of mammographic density were performed using ImageJ, a fully automated thresholding technique. The associations of SNPs to densities were analyzed using linear regression models.

RESULTS

We successfully evaluated the associations of 36 SNPs with mammographic densities. After adjusting for age, body mass index, parity, and menopausal status, we found that in our cohort of 865 Malaysian Chinese, three SNPs in the 6q25.1 region near ESR1 (rs2046210, rs12173570, and rs10484919) that were associated with mammographic density, breast cancer risk, or breast size in previous GWAS were significantly associated with both percentage density and absolute dense area. We could not replicate the most significant association found previously in European women (rs10995190, ZNF365 gene) because the minor allele was absent for Asian women.

CONCLUSION

We found that the directions of genetic associations were similar to those reported in Caucasian women.

IMPACT

Our results show that even in Asian women with lower population risk to breast cancer, there is shared heritability between mammographic density and breast cancer risk.

Breast reconstruction following conservative mastectomies: predictors of complications and outcomes

Breast reconstruction can be performed using a variety of techniques, most commonly categorized into an alloplastic approach or an autologous tissue method. Both strategies have certain risk factors that influence reconstructive outcomes and complication rates. In alloplastic breast reconstruction, surgical outcomes and complication rates are negatively impacted by radiation, smoking, increased body mass index (BMI), hypertension, and prior breast conserving therapy. Surgical factors such as the type of implant material, undergoing immediate breast reconstruction, and the use of fat grafting can improve patient satisfaction and aesthetic outcomes. In autologous breast reconstruction, radiation, increased BMI, certain previous abdominal surgery, smoking, and delayed reconstruction are associated with higher complication rates. Though a pedicled transverse rectus abdominis myocutaneous (TRAM) flap is the most common type of flap used for autologous breast reconstruction, pedicled TRAMs are more likely to be associated with fat necrosis than a free TRAM or deep inferior epigastric perforator (DIEP) flap. Fat grafting can also be used to improve aesthetic outcomes in autologous reconstruction. This article focuses on factors, both patient and surgical, that are predictors of complications and outcomes in breast reconstruction.

A twin study of breastfeeding with a preliminary genome-wide association scan

Breastfeeding has been an important survival trait during human history, though it has long been recognized that individuals differ in their exact breastfeeding behavior. Here our aims were, first, to explore to what extent genetic and environmental influences contributed to the individual differences in breastfeeding behavior; second, to detect possible genetic variants related to breastfeeding; and lastly, to test if the genetic variants associated with breastfeeding have been previously found to be related with breast size. Data were collected from a large community-based cohort of Australian twins, with 3,364 women participating in the twin modelling analyses and 1,521 of them included in the genome-wide association study (GWAS). Monozygotic (MZ) twin correlations (r MZ = 0.52, 95% CI 0.46-0.57) were larger than dizygotic (DZ) twin correlations (r DZ = 0.35, 95% CI 0.25-0.43) and the best-fitting model was the one composed by additive genetics and unique environmental factors, explaining 53% and 47% of the variance in breastfeeding behavior, respectively. No breastfeeding-related genetic variants reached genome-wide significance. The polygenic risk score analyses showed no significant results, suggesting breast size does not influence breastfeeding. This study confers a replication of a previous one exploring the sources of variance of breastfeeding and, to our knowledge, is the first one to conduct a GWAS on breastfeeding and look at the overlap with variants for breast size.

Breast cancer mortality vs. exercise and breast size in runners and walkers

Purpose

Identify predictors of breast cancer mortality in women who exercised below (<7.5 metabolic equivalent hours/week, MET-hours/wk), at (7.5 to 12.5 MET-hours/wk), or above (≥12.5 MET-hours/wk) recommended levels.

Methods

Cox proportional hazard analyses of baseline pre-diagnosis MET-hours/wk vs. breast cancer mortality adjusted for follow-up age, race, baseline menopause, and estrogen and oral contraceptive use in 79,124 women (32,872 walkers, 46,252 runners) from the National Walkers' and Runners' Health Studies.

Results

One-hundred eleven women (57 walkers, 54 runners) died from breast cancer during the 11-year follow-up. The decline in mortality in women who exercised ≥7.5 MET-hours/wk was not different for walking and running (P = 0.34), so running and walking energy expenditures were combined. The risk for breast cancer mortality was 41.5% lower for ≥7.5 vs. <7.5 MET-hours/wk (HR: 0.585, 95%CI: 0.382 to 0.924, P = 0.02), which persisted when adjusted for BMI (HR: 0.584, 95%CI: 0.368 to 0.956, P = 0.03). Other than age and menopause, baseline bra cup size was the strongest predictor of breast cancer mortality, i.e., 57.9% risk increase per cup size when adjusted for MET-hours/wk and the other covariates (HR: 1.579, 95%CI: 1.268 to 1.966, P<0.0001), and 70.4% greater when further adjusted for BMI (HR: 1.704, 95%CI: 1.344 to 2.156, P = 10⁻⁵). Breast cancer mortality was 4.0-fold greater (HR: 3.980, 95%CI: 1.894 to 9.412, P = 0.0001) for C-cup, and 4.7-fold greater (HR: 4.668, 95%CI: 1.963 to 11.980, P = 0.0004) for ≥D-cup vs. A-cup when adjusted for BMI and other covariates. Adjustment for cup size and BMI did not eliminate the association between breast cancer mortality and ≥7.5 MET-hour/wk walked or run (HR: 0.615, 95%CI: 0.389 to 1.004, P = 0.05).

Conclusion

Breast cancer mortality decreased in association with both meeting the exercise recommendations and smaller breast volume.

Large-scale genotyping identifies a new locus at 22q13.2 associated with female breast size

BACKGROUND

Individual differences in breast size are a conspicuous feature of variation in human females and have been associated with fecundity and advantage in selection of mates. To identify common variants that are associated with breast size, we conducted a large-scale genotyping association meta-analysis in 7169 women of European descent across three independent sample collections with digital or screen film mammograms.

METHODS

The samples consisted of the Swedish KARMA, LIBRO-1 and SASBAC studies genotyped on iCOGS, a custom illumina iSelect genotyping array comprising of 211 155 single nucleotide polymorphisms (SNPs) designed for replication and fine mapping of common and rare variants with relevance to breast, ovary and prostate cancer. Breast size of each subject was ascertained by measuring total breast area (mm(2)) on a mammogram.

RESULTS

We confirm genome-wide significant associations at 8p11.23 (rs10086016, p=1.3×10(-14)) and report a new locus at 22q13 (rs5995871, p=3.2×10(-8)). The latter region contains the MKL1 gene, which has been shown to impact endogenous oestrogen receptor α transcriptional activity and is recruited on oestradiol sensitive genes. We also replicated previous genome-wide association study findings for breast size at four other loci.

CONCLUSIONS

A new locus at 22q13 may be associated with female breast size.

Breast size, thoracic kyphosis & thoracic spine pain - association & relevance of bra fitting in post-menopausal women: a correlational study

BACKGROUND

Menopause would seem to exist as a period of accelerated changes for women and their upper torso mechanics. Whether these anthropometric changes reflect changes in pain states remains unclear. Plausible mechanisms of pain exist for the independent and combined effect of increasing breast size and thoracic kyphosis. Bra fit has the potential to change when the anthropometric measures (chest circumference and bust circumference) used to determine bra size change, such as postmenopausally.Identifying an association between breast size, thoracic kyphosis and thoracic spine pain in postmenopausal women and identifying the relevance of bra fit to this association may be of importance to the future management and education of post-menopausal women presenting clinically with thoracic spine pain.

METHODS

A cross-sectional study design. Fifty-one postmenopausal bra-wearing women were recruited. Measures included breast size (Triumph International), thoracic kyphosis (flexible curve), bra fitted (Y/N) and pain (Short Form McGill Pain Questionnaire) and tenderness on palpation (posteroanterior pressure testing). These measures were collected in one session at a physiotherapy clinic.

RESULTS

The majority of the women in this study were overweight or obese and wearing an incorrect sized bra. Pain was significantly related to breast size, body weight and BMI at mid thoracic levels (T7-8). In contrast self-reported thoracic pain was not correlated with age or index of kyphosis (thoracic kyphosis). Women with thoracic pain were no more likely to have their bra professionally fitted whereas women with a higher BMI and larger breasts were more likely to have their bra professionally fitted.

CONCLUSION

The findings of this study show that larger breasts and increased BMI are associated with thoracic pain in postmenopausal women. This is unrelated to thoracic kyphosis. Increasing breast size and how a bra is worn may have biomechanical implications for the loaded thoracic spine and surrounding musculature. Post-menopause women present with a spectrum of anthropometrical changes that have the potential to contribute to altered biomechanics and affect pain states in the thoracic spine.

Resource security impacts men's female breast size preferences

It has been suggested human female breast size may act as signal of fat reserves, which in turn indicates access to resources. Based on this perspective, two studies were conducted to test the hypothesis that men experiencing relative resource insecurity should perceive larger breast size as more physically attractive than men experiencing resource security. In Study 1, 266 men from three sites in Malaysia varying in relative socioeconomic status (high to low) rated a series of animated figures varying in breast size for physical attractiveness. Results showed that men from the low socioeconomic context rated larger breasts as more attractive than did men from the medium socioeconomic context, who in turn perceived larger breasts as attractive than men from a high socioeconomic context. Study 2 compared the breast size judgements of 66 hungry versus 58 satiated men within the same environmental context in Britain. Results showed that hungry men rated larger breasts as significantly more attractive than satiated men. Taken together, these studies provide evidence that resource security impacts upon men’s attractiveness ratings based on women’s breast size.

Determinants of breast appearance and aging in identical twins

BACKGROUND

Appearance, aging, and disorders of the breast are multifactorial. There are intrinsic, patient-specific characteristics, such as breast growth during puberty and propensity for breast cancer, which are primarily inherited. There are also environmental factors, which can be potentially controlled. Monozygotic twins provide an excellent research opportunity to examine the role of extrinsic factors in subjects with identical genetic predispositions.

OBJECTIVES

The authors investigate the role and significance of various environmental and acquired factors on breast aesthetics.

METHODS

Identical female twins were recruited during the Twins Days Festival in Twinsburg, Ohio, in 2009 and 2010. After consent was obtained, enrolled subjects completed a comprehensive survey on their medical and personal history. Standardized digital photographs were taken by medical photographers. Sixteen aesthetic breast features were subjectively rated by 6 plastic surgery residents blinded to the survey results. These ratings were then analyzed against survey data to determine the significance of different exogenous factors on breast appearance.

RESULTS

A total of 161 pairs of identical female twins (n = 322) with a mean (SD) age of 47.6 (14.5) years were recruited. Twins who moisturized their skin daily had significantly fewer rhytids (P = .002). Twins who received hormone replacement therapy after menopause had more attractive breast shape, size, projection, areolar shape, and areolar size (P < .03). However, twins who had a higher body mass index, greater number of pregnancies, and larger cup sizes had significantly less attractive breasts (P < .05). Twins who smoked cigarettes and consumed alcohol also had significantly less attractive breasts (P < .05). Twins who breastfed had less attractive areolar size and shape but better skin quality than their counterparts who never breastfed (P < .03). Finally, there was a significantly higher incidence of breast pain in twins who primarily slept on their sides compared with twins who primarily slept on their backs (P < .008).

CONCLUSIONS

This study implicates several environmental factors that significantly affect the aesthetic quality of breasts.

Genetic variants associated with breast size also influence breast cancer risk

BACKGROUND

While some factors of breast morphology, such as density, are directly implicated in breast cancer, the relationship between breast size and cancer is less clear. Breast size is moderately heritable, yet the genetic variants leading to differences in breast size have not been identified.

METHODS

To investigate the genetic factors underlying breast size, we conducted a genome-wide association study (GWAS) of self-reported bra cup size, controlling for age, genetic ancestry, breast surgeries, pregnancy history and bra band size, in a cohort of 16,175 women of European ancestry.

RESULTS

We identified seven single-nucleotide polymorphisms (SNPs) significantly associated with breast size (p<5.10(-8)): rs7816345 near ZNF703, rs4849887 and (independently) rs17625845 flanking INHBB, rs12173570 near ESR1, rs7089814 in ZNF365, rs12371778 near PTHLH, and rs62314947 near AREG. Two of these seven SNPs are in linkage disequilibrium (LD) with SNPs associated with breast cancer (those near ESR1 and PTHLH), and a third (ZNF365) is near, but not in LD with, a breast cancer SNP. The other three loci (ZNF703, INHBB, and AREG) have strong links to breast cancer, estrogen regulation, and breast development.

CONCLUSIONS

These results provide insight into the genetic factors underlying normal breast development and show that some of these factors are shared with breast cancer. While these results do not directly support any possible epidemiological relationships between breast size and cancer, this study may contribute to a better understanding of the subtle interactions between breast morphology and breast cancer risk.

The relationship between breast size and anthropometric characteristics

OBJECTIVES

Current clinical selection criteria for mammaplasty use weight-related parameters, and weight loss is recommended as a nonsurgical intervention to reduce breast size. However, research has not firmly established if breast size is related to body size and composition. This study aims to investigate anthropometric characteristics in smaller and larger breasted women and identify predictors of breast mass.

METHODS

A bra fitter determined underband and cup size of 93 A to H cup size women (mean ± standard deviation, age 25.7 ± 5.6 years, height 1.67 ± 0.6 cm, and mass 65.6 ± 11.0 kg). Estimations of breast mass (g) were made, and participants were categorized as smaller (<500 g) or larger (>500 g) breasted. Restricted anthropometric profiles determined body mass, height, body mass index (BMI), waist-to-hip ratio, sum of eight skinfolds, subscapular to triceps skinfold ratio, somatotype, percent body fat, fat and fat-free mass, and suprasternal notch to nipple distance.

RESULTS

All variables (excluding height, subscapular to triceps skinfold ratio, and age) were significantly greater in larger breasted women. Body mass-related parameters and suprasternal notch to nipple distance were positively related to breast mass, with BMI and suprasternal notch to nipple distance accounting for half of the variance in breast mass.

CONCLUSION

Smaller and larger breasted women demonstrate differences in anthropometry, with body mass and BMI demonstrating strong relationships to breast mass. Measures of BMI and suprasternal notch to nipple distance enable predictions of breast mass and suggest that weight-related parameters are not appropriate exclusion criteria for mammaplasty.