Birth size and colorectal cancer risk: a prospective population based study

Changing epidemiology of colorectal cancer - birth cohort effects and emerging risk factors

Incidence and mortality of colorectal cancer (CRC) are increasing worldwide, suggesting broad changes in the epidemiology of CRC. In this Review, we discuss the changes that are becoming evident, including trends in CRC incidence and mortality by age and birth cohort, and consider the contributions of early-life exposures and emerging risk factors to these changes. Importantly, incidence of CRC has increased among people born since the early 1950s in nearly all regions of the world. These so-called birth cohort effects imply the involvement of factors that influence the earliest stages of carcinogenesis and have effects across the life course. Accumulating evidence supports the idea that early-life exposures are important risk factors for CRC, including exposures during fetal development, childhood, adolescence and young adulthood. Environmental chemicals could also have a role because the introduction of many in the 1950s and 1960s coincides with increasing incidence of CRC among people born during those years. To reverse the expected increases in the global burden of CRC, participation in average-risk screening programmes needs to be increased by scaling up and implementing evidence-based screening strategies, and emerging risk factors responsible for these increases need to be identified.

Birth weight, adult body size, and risk of colorectal cancer

BACKGROUND

Evidence suggests that birth weight may be associated with colorectal cancer (CRC) risk later in life. Whether the association is mediated by adult body size remains unexamined.

METHOD

Cox proportional hazards models (Hazard Ratio (HR) and 95 % Confidence Intervals (CI)) were used to evaluate the association between self-reported birth weight (<6 lbs, 6-<8 lbs, ≥8 lbs) and CRC risk among 70,397 postmenopausal women from the Women's Health Initiative. Further, we assessed whether this association was mediated by adult body size using multiple mediation analyses.

RESULTS

Compared with birth weights of 6-< 8 lbs, birth weight ≥ 8 lbs was associated with higher CRC risk in postmenopausal women (HR = 1.31, 95 % CI 1.16-1.48). This association was significantly mediated by adult height (proportion mediated =11.4 %), weight (11.2 %), waist circumference (10.9 %), and body mass index at baseline (4.0 %). The joint effect of adult height and weight explained 21.6 % of this positive association.

CONCLUSION

Our data support the hypothesis that the intrauterine environment and fetal development may be related to the risk of developing CRC later in life. While adult body size partially explains this association, further investigation is required to identify other factors that mediate the link between birth weight and CRC.

Maternal obesity, pregnancy weight gain, and birth weight and risk of colorectal cancer

OBJECTIVE

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide. Obesity is a well-established risk factor for CRC, and fetal or developmental origins of obesity may underlie its effect on cancer in adulthood. We examined associations of maternal obesity, pregnancy weight gain, and birth weight and CRC in adult offspring.

DESIGN

The Child Health and Development Studies is a prospective cohort of women receiving prenatal care between 1959 and 1966 in Oakland, California (N=18 751 live births among 14 507 mothers). Clinical information was abstracted from mothers' medical records 6 months prior to pregnancy through delivery. Diagnoses of CRC in adult (age ≥18 years) offspring were ascertained through 2019 by linkage with the California Cancer Registry. We used Cox proportional hazards models to estimate adjusted HR (aHR); we examined effect measure modification using single-referent models to estimate the relative excess risk due to interaction (RERI).

RESULTS

68 offspring were diagnosed with CRC over 738 048 person-years of follow-up, and half (48.5%) were diagnosed younger than age 50 years. Maternal obesity (≥30 kg/m²) increased the risk of CRC in offspring (aHR 2.51, 95% CI 1.05 to 6.02). Total weight gain modified the association of rate of early weight gain (RERI -4.37, 95% CI -9.49 to 0.76), suggesting discordant growth from early to late pregnancy increases risk. There was an elevated association with birth weight (≥4000 g: aHR 1.95, 95% CI 0.8 to 4.38).

CONCLUSION

Our results suggest that in utero events are important risk factors for CRC and may contribute to increasing incidence rates in younger adults.

Gut DYSBIOSIS and altered barrier function precedes the appearance of metabolic syndrome in a rat model of nutrient-induced catch-up growth

Nutritional restriction early in life followed by catch-up growth has been associated with increased risk of metabolic syndrome in adulthood. To elucidate whether altered gut colonization underlies the mechanisms responsible of this predisposition gut microbiome was studied before or afterwards catch-up growth. Offspring of dams fed ad libitum (C) or undernourished during pregnancy and suckling (U), were weaned onto high-fat diet (HFD) for 22 weeks (CHF and UHF, respectively) or continued on their diet. HF-feeding induced glucose intolerance (P<.05), insulin resistance (P<.001), and white adipose tissue inflammation (P<.001) in UHF rats compared to CHF. Analyses of gut microbial composition before catch-up growth revealed reduced F/B ratio and significant expansion of the mucolytic genera Akkermansia (P<.05) and Desulfovibrio (P<.05) in U pups. Although relative abundance of Akkermansia remained elevated to adulthood in U rats, HFD normalized its levels to C and CHF. Food-restriction increased intestinal permeability causing disorganization on the tight-junction proteins of colonic epithelium, Zonula Occludens-1 (ZO-1) and occludin, and reducing the mucus thickness layer in U adult rats. The levels of ZO-1 and occludin were not recovered in U rats after HF-feeding. This event was correlated with increased circulating levels of bacterial lipopolysaccharides in both U and UHF adult rats. Even more, serum lipopolysaccharides were already elevated in U rats compared to C group (P<.001) at weaning. Thus, gut dysbiosis and chronic endotoxemia observed in U rats, even before catch-up growth, might anticipate a pro-inflammatory milieu promoting metabolic diseases when fed hyperlipidic diets.

Impact of maternal reproductive factors on cancer risks of offspring: A systematic review and meta-analysis of cohort studies

Background

A number of studies have reported on associations between reproductive factors, such as delivery methods, number of birth and breastfeeding, and incidence of cancer in children, but systematic reviews addressing this issue to date have important limitations, and no reviews have addressed the impact of reproductive factors on cancer over the full life course of offspring.

Methods

We performed a comprehensive search in MEDLINE, and Embase up to January 2020 and Web of Science up to 2018 July, including cohort studies reporting the association between maternal reproductive factors of age at birth, birth order, number of births, delivery methods, and breastfeeding duration and cancer in children. Teams of two reviewers independently extracted data and assessed risk of bias. We conducted random effects meta-analyses to estimate summary relative estimates, calculated absolute differences between those with and without risk factors, and used the GRADE approach to evaluate the certainty of evidence.

Results

For most exposures and most cancers, we found no suggestion of a causal relation. We found low to very low certainty evidence of the following very small possible impact: higher maternal age at birth with adult multiple myeloma and lifetime uterine cervix cancer incidence; lower maternal age at birth with childhood overall cancer mortality (RR = 1.15, 95% CI = 1.01–1.30; AR/10,000 = 1, 95% CI = 0 to 2), adult leukemia and lifetime uterine cervix cancer incidence; higher birth order with adult melanoma, cervix uteri, corpus uteri, thyroid cancer incidence, lifetime lung, corpus uteri, prostate, testis, sarcoma, thyroid cancer incidence; larger number of birth with childhood brain (RR = 1.27, 95% CI = 1.06–1.52; AR/10,000 = 1, 95% CI = 0 to 2), leukemia (RR = 2.11, 95% CI = 1.62–2.75; AR/10,000 = 9, 95% CI = 5 to 14), lymphoma (RR = 4.66, 95% CI = 1.40–15.57; AR/10,000 = 11, 95% CI = 1 to 44) incidence, adult stomach, corpus uteri cancer incidence and lung cancer mortality, lifetime stomach, lung, uterine cervix, uterine corpus, multiple myeloma, testis cancer incidence; Caesarean delivery with childhood kidney cancer incidence (RR = 1.25, 95% CI = 1.01–1.55; AR/10,000 = 0, 95% CI = 0 to 1); and breastfeeding with adult colorectal cancer incidence.

Conclusion

Very small impacts existed between a number of reproductive factors and cancer incidence and mortality in children and the certainty of evidence was low to very low primarily due to observational design.

Epidemiology and Mechanisms of the Increasing Incidence of Colon and Rectal Cancers in Young Adults

In contrast to the decreasing incidence of colorectal cancer (CRC) in older populations, the incidence has nearly doubled in younger adults since the early 1990s. Approximately 1 in 10 new diagnoses of CRC are now made in individuals 50 years or younger. Patients' risk of CRC has been calculated largely by age and family history, yet 3 of 4 patients with early-onset CRC have no family history of the disease. Rapidly increasing incidence rates in younger people could result from generational differences in diet, environmental exposures, and lifestyle factors. We review epidemiologic trends in CRC, data on genetic and nongenetic risk factors, and new approaches for determining CRC risk. These may identify individuals likely to benefit from early screening and specialized surveillance.

Early Life Exposures and Adult Cancer Risk

Very little is known about the influence of early life exposures on adult cancer risk. The purpose of this narrative review was to summarize the epidemiologic evidence relating early life tobacco use, obesity, diet, and physical activity to adult cancer risk; describe relevant theoretical frameworks and methodological strategies for studying early life exposures; and discuss policies and research initiatives focused on early life. Our findings suggest that in utero exposures may indirectly influence cancer risk by modifying biological pathways associated with carcinogenesis; however, more research is needed to firmly establish these associations. Initiation of exposures during childhood and adolescence may impact cancer risk by increasing duration and lifetime exposure to carcinogens and/or by acting during critical developmental periods. To expand the evidence base, we encourage the use of life course frameworks, causal inference methods such as Mendelian randomization, and statistical approaches such as group-based trajectory modeling in future studies. Further, we emphasize the need for objective exposure biomarkers and valid surrogate endpoints to reduce misclassification. With the exception of tobacco use, there is insufficient evidence to support the development of new cancer prevention policies; however, we highlight existing policies that may reduce the burden of these modifiable risk factors in early life.

Cord Blood Metabolic Signatures of Birth Weight: A Population-Based Study

Birth weight is an important indicator of maternal and fetal health and a predictor of health in later life. However, the determinants of variance in birth weight are still poorly understood. We aimed to identify the biological pathways, which may be perturbed by environmental exposures, that are important in determining birth weight. We applied untargeted mass-spectrometry-based metabolomics to 481 cord blood samples collected at delivery in four birth cohorts from across Europe: ENVIRONAGE (Belgium), INMA (Spain), Piccolipiu (Italy), and Rhea (Greece). We performed a metabolome-wide association scan for birth weight on over 4000 metabolic features, controlling the false discovery rate at 5%. Annotation of compounds was conducted through reference to authentic standards. We identified 68 metabolites significantly associated with birth weight, including vitamin A, progesterone, docosahexaenoic acid, indolelactic acid, and multiple acylcarnitines and phosphatidylcholines. We observed enrichment (p < 0.05) of the tryptophan metabolism, prostaglandin formation, C21-steroid hormone signaling, carnitine shuttle, and glycerophospholipid metabolism pathways. Vitamin A was associated with both maternal smoking and birth weight, suggesting a mediation pathway. Our findings shed new light on the pathways central to fetal growth and will have implications for antenatal and perinatal care and potentially for health in later life.

Feasibility of Linking Long-Term Cardiovascular Cohort Data to Offspring Birth Records: The Bogalusa Heart Study

Introduction Researchers in perinatal health, as well as other areas, may be interested in linking existing datasets to vital records data when the existence or timing of births is unknown. Methods 5914 women who participated in the Bogalusa Heart Study (1973-2009), a long-running study of cardiovascular health in childhood, adolescence, and adulthood, were linked to vital statistics birth data from Louisiana, Mississippi, and Texas (1982-2010). Deterministic and probabilistic linkages based on social security number, race, maternal date of birth, first name, last name, and Soundex codes for name were conducted. Characteristics of the linked and unlinked women were compared using t-tests, Chi square tests, and multiple regression with adjustment for age and year of examinations. Results The Louisiana linkage linked 4876 births for 2770 women; Mississippi linked 791 births to 487 women; Texas linked 223 births to 153 women; After removal of duplicates and implausible dates, this left a total of 5922 births to 3260 women. This represents a successful linkage of 55% of all women ever seen in the larger study, and an estimated 65% of all women expected to have given birth. Those linked had more study visits, were more likely to be black, and had statistically lower BMIs than unlinked participants. Discussion Linking unrelated study data to vital records data was feasible to a degree. The linked group had a somewhat more favorable health profile and was less mobile than the overall study population.

A Comprehensive Model of Colorectal Cancer by Risk Factor Status and Subsite Using Data From the Nurses' Health Study

We expanded and updated our colon cancer risk model to evaluate colorectal cancer (CRC) and whether subsite-specific risk models are warranted. Using data from 1980-2010 for 90,286 women enrolled in the Nurses' Health Study, we performed competing-risks regression and tests for subsite heterogeneity (proximal colon: n = 821; distal colon: n = 521; rectum: n = 376). Risk factors for CRC were consistent with those in our colon cancer model. Processed meat consumption was associated with a higher risk of distal (hazard ratio (HR) = 1.45; P = 0.02) but not proximal (HR = 0.95; P = 0.72) colon cancer. Smoking was associated with both colon (HR = 1.21) and rectal (HR = 1.27) cancer and was more strongly associated with proximal (HR = 1.31) than with distal (HR = 1.04) colon cancer (P = 0.029). We observed a significant trend of cancer risk for smoking in subsites from the cecum (HR = 1.41) to the proximal colon (excluding the cecum; HR = 1.27) to the distal colon (HR = 1.04; P for trend = 0.040). The C statistics for colorectal (C = 0.607), colon (C = 0.603), and rectal (C = 0.639) cancer were similar, although C was slightly higher for rectal cancer. Despite evidence for site-specific differences for several risk factors, overall our findings support the application of risk prediction models for colon cancer to CRC.

Associations between birth weight and colon and rectal cancer risk in adulthood

BACKGROUND

Birth weight has inconsistent associations with colorectal cancer, possibly due to different anatomic features of the colon versus the rectum. The aim of this study was to investigate the association between birth weight and colon and rectal cancers separately.

METHODS

193,306 children, born from 1936 to 1972, from the Copenhagen School Health Record Register were followed prospectively in Danish health registers. Colon and rectal cancer cases were defined using the International Classification of Disease version 10 (colon: C18.0-18.9, rectal: 19.9 and 20.9). Only cancers classified as adenocarcinomas were included in the analyses. Cox regressions were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Analyses were stratified by birth cohort and sex.

RESULTS

During 3.8 million person-years of follow-up, 1465 colon and 961 rectal adenocarcinomas were identified. No significant sex differences were observed; therefore combined results are presented. Birth weight was positively associated with colon cancers with a HR of 1.14 (95% CI, 1.04-1.26) per kilogram of birth weight. For rectal cancer a significant association was not observed for birth weights below 3.5kg. Above 3.5kg an inverse association was observed (at 4.5kg, HR=0.77 [95% CI, 0.61-0.96]). Further, the associations between birth weight and colon and rectal cancer differed significantly from each other (p=0.006).

CONCLUSIONS

Birth weight is positively associated with the risk of adult colon cancer, whereas the results for rectal cancer were inverse only above values of 3.5kg. The results underline the importance of investigating colon and rectal cancer as two different entities.

Birth weight and adult cancer incidence: large prospective study and meta-analysis

BACKGROUND

Most evidence about associations between birth weight and adult cancer risk comes from studies linking birth records to cancer registration data, where information on known risk factors for cancer is generally lacking. Here, we report on associations between birth weight and cause-specific cancer risk in a large cohort of UK women, and investigate how observed associations are affected by other factors.

METHODS

A total of 453 023 women, born in the 1930s and 1940s, reported their birth weight, maternal smoking, parental heights, age at menarche, adult height, adult smoking, and many other personal characteristics. They were followed for incident cancer. Using Cox regression, relative risks by birth weight were estimated for cancers with more than 1500 incident cases, adjusting for 17 potential confounding factors, individually and simultaneously.

RESULTS

Birth weight reported in adulthood was strongly correlated with that recorded at birth (correlation coefficient = 0.78, P < 0.0001). Reported birth weight was associated with most of the potential confounding factors examined, the strongest association being with adult height. After 9.2 years follow-up per woman, 39 060 incident cancers were registered (4414 colorectal, 3175 lung, 1795 malignant melanoma, 14 542 breast, 2623 endometrial, 2009 ovarian, 1565 non-Hodgkin lymphoma, and 8937 other cancers). Associations with birth weight were null or weak and reduced after adjustment by adult height (P[trend] > 0.01 for every cancer, after adjustment). In contrast, adult height was strongly related to the risk of every cancer except lung cancer, after adjusting for birth weight and other factors (P[trend] < 0.0001 for most cancers). For lung cancer, adjusting for smoking reduced the association with birth weight. Meta-analyses were dominated by our findings.

CONCLUSION

Birth weight and adult height are correlated and likely to be markers of some aspect of growth that affects cancer risk in adulthood. However, birth weight adds little, if any, additional information to adult height as a predictor of cancer incidence in women.

The shape of the placental surface at birth and colorectal cancer in later life

OBJECTIVES

Many chronic diseases, including certain cancers, may originate through variations in the supply of nutrients to the fetus. These variations change gene expression and permanently set the structure and function of the body, a process known as programming. Fetal nutrition depends on the mother's metabolism and nutritional reserves, and on the placenta's ability to transfer nutrients from mother to baby. In this study, we examine how colorectal cancer is related to maternal and placental characteristics.

METHODS

We ascertained 275 cases of colorectal cancer among the 20,431 people in the Helsinki Birth Cohort, who were born during 1924-1944 and whose body size at birth was recorded, together with the shape and size of the placenta.

RESULTS

Hazard ratios for colorectal cancer increased as the placental surface became longer and more oval. The hazard ratio was 2.3 (95% CI 1.2-4.7) among people in whom the difference between the length and breadth of the surface exceeded 6 cm, compared with those in whom there was no difference. Colorectal cancer was unrelated to other placental measurements or to body size at birth.

CONCLUSION

An oval placental surface at birth is associated with later colorectal cancer. The shape of the placental surface is determined by events at around 8-12 weeks gestation. We speculate that, if the spiral arteries open prematurely, the surface becomes more oval and the fetus is at risk of oxidative damage at a time when the colon is differentiating.

The maternal womb: a novel target for cancer prevention in the era of the obesity pandemic?

The dramatic rise in worldwide prevalence of obesity has necessitated the search for more efficacious antiobesity strategies to counter the increased cancer risks in overweight and obese individuals. The mechanistic pathways linking obesity status with adult chronic diseases such as cancer remain incompletely understood. A growing body of evidence suggests that novel approaches and interventional agents to disrupt the feed-forward cycle of maternal to offspring obesity transfer that is initiated in utero will be important for stemming both the obesity pandemic and the associated increase in cancer incidence. The convergence of multiple research areas including those encompassing the insulin and insulin-like growth factor systems, epigenetics, and stem cell biology is providing insights into the potential for cancer prevention in adult offspring previously exposed to the intrauterine environment of overweight/obese mothers. Here, we review the current state of this nascent research field, with a focus on three major cancers, namely breast, colorectal, and liver, and suggest some possible future directions to optimize its impact for the health of future generations.

Fetal origins of adult disease

Dr. David Barker first popularized the concept of fetal origins of adult disease (FOAD). Since its inception, FOAD has received considerable attention. The FOAD hypothesis holds that events during early development have a profound impact on one's risk for development of future adult disease. Low birth weight, a surrogate marker of poor fetal growth and nutrition, is linked to coronary artery disease, hypertension, obesity, and insulin resistance. Clues originally arose from large 20th century, European birth registries. Today, large, diverse human cohorts and various animal models have extensively replicated these original observations. This review focuses on the pathogenesis related to FOAD and examines Dr. David Barker's landmark studies, along with additional human and animal model data. Implications of the FOAD extend beyond the low birth weight population and include babies exposed to stress, both nutritional and nonnutritional, during different critical periods of development, which ultimately result in a disease state. By understanding FOAD, health care professionals and policy makers will make this issue a high health care priority and implement preventive measures and treatment for those at higher risk for chronic diseases.

Intrauterine growth restriction not only modifies the cecocolonic microbiota in neonatal rats but also affects its activity in young adult rats

OBJECTIVE

Elucidating why intrauterine growth restriction (IUGR) predisposes to some intestinal pathologies would help in their prevention. Intestinal microbiota could be involved in this predisposition; its initial setup is likely to be altered by IUGR because IUGR delays perinatal intestinal development and strongly interacts with intestinal physiology. Furthermore, because initial colonization determines adult intestinal microbiota, an IUGR-induced defect in initial microbiota would have long-term consequences. Thus, to characterize the effect of IUGR on intestinal microbiota, we compared the composition and activity of cecocolonic microbiota from birth to adulthood in rats with and without IUGR.

MATERIALS AND METHODS

IUGR was induced by gestational isocaloric protein restriction. Pups were fed by unrestricted lactating mothers. At different ages (days 5, 12, 16, 22, 40, and 100), cecocolonic contents from rats with IUGR and controls were analyzed for concentrations of bacterial end products and numbers of main bacterial groups, and submitted to in vitro fermentation tests.

RESULTS

IUGR affected gut colonization: bacterial density was increased at day 5 and decreased at day 12. In adulthood, rats with IUGR still differed from controls, harboring fewer Bifidobacterium sp at day 40 and more bacteria related to Roseburia intestinalis at day 100. In vivo, propionate concentration was decreased by IUGR before weaning, whereas the concentrations of other short-chain fatty acids were decreased at day 40, although the in vitro metabolic capability was unaffected overall.

CONCLUSIONS

We showed that IUGR induced, per se, some neonatal and long-lasting alterations of the intestinal microbiota. The physiological consequences of these changes and their relation to the predisposing effect of IUGR to gut pathologies must now be explored.

Intrauterine growth restriction alters postnatal colonic barrier maturation in rats

Intrauterine growth restriction (IUGR) is a leading cause of perinatal mortality and morbidity and increases the risk for necrotizing enterocolitis. We hypothesized that colonic barrier disruption could be responsible for intestinal frailty in infants and adults born with IUGR. Mucins and trefoil factor family 3 (TFF3) actively contribute to epithelium protection and healing. Our aim was to determine whether IUGR affects colonic mucosa maturation. IUGR was induced by dietary protein restriction in pregnant dams. Mucins and Tff3 expression and morphologic maturation of the colonic mucosa were followed during postnatal development of the offspring. Before weaning, mucin 2 and Tff3 protein levels were reduced in colonic mucosa of rats with IUGR compared with controls. After weaning, expression of mucin 2 (mRNA and protein) and mucin 4 (mRNA) were lower in colonic mucosa of rats with IUGR. At the same time, IUGR was associated with a reduction of crypt depth and a higher percentage of crypts in fission. We conclude that IUGR impairs mucus barrier development and is associated with long-term alterations of mucin expression. The lack of an efficient colonic barrier induced by IUGR may predispose to colonic injury not only in neonatal life but also in later life.

Birth characteristics and risk of colorectal cancer: a study among Swedish twins

Type-2 diabetes increases the risk of colorectal cancer, and is also associated with low birth weight. However, we found no evidence of associations between birth characteristics and risk of colorectal cancer (m=248) among Swedish twins.

Correlation of umbilical cord blood haematopoietic stem and progenitor cell levels with birth weight: implications for a prenatal influence on cancer risk

We examined the relation with birth weight and umbilical cord blood concentrations of haematopoietic stem and progenitor populations in 288 singleton infants. Across the whole range of birth weight, there was a positive relation between birth weight and CD34⁺CD38⁻ cells, with each 500 g increase in birth weight being associated with a 15.5% higher (95% confidence interval: 1.6–31.3%) cell concentration. CD34⁺ and CD34⁺c-kit⁺ cells had J-shaped relations and CFU-GM cells had a U-shaped relation with birth weight. Among newborns with ⩾3000 g birth weights, concentrations of these cells increased with birth weight, while those below 3000 g had higher stem cell concentrations than the reference category of 3000–3499 g. Adjustment for cord blood plasma insulin-like growth factor-1 levels weakened the stem and progenitor cell–birth weight associations. The positive associations between birth weight and stem cell measurements for term newborns with a normal-to-high birth weight support the stem cell burden hypothesis of cancer risk.

Birth weight and risk of cancer

BACKGROUND

It is well established that prenatal biologic processes are important for the development of some childhood cancers, whereas less is known regarding their influence on adult cancer risk. High birth weight has been associated with risk of breast cancer, whereas studies of other specific cancers and all cancers together have been less conclusive.

METHODS

The authors established a cohort of more than 200,000 men and women who were born between 1936 and 1975. Birth weights were obtained from school health records and information concerning cancer from the Danish Cancer Registry. Follow-up was performed between April 1, 1968 and December 31, 2003. During 6,975,553 person-years of follow-up, a total of 12,540 primary invasive cancers were diagnosed.

RESULTS

Analyses of site-specific cancers revealed that the majority of cancers had a positive linear association with birth weight. Departures from a positive linear association were found to be statistically significant for cancers of the pancreas and bladder, which demonstrated a V-shaped association, and testicular cancer, which demonstrated an inverse association with birth weight. Excluding these 3 exceptions, the trends for the individual cancer sites were not heterogeneous, and the overall trend was a relative risk of 1.07 (95% confidence interval, 1.03-1.11) per 1000-g increase in birth weight. This trend was the same in men and women and in all age groups.

CONCLUSIONS

A 7% increase in cancer risk was observed per 1000-g increase in birth weight. Few cancers demonstrated a nonlinear association with birth weight, and testicular cancer was found to be negatively associated with birth weight. The authors hypothesized that the biologic explanation behind the association between birth weight and cancer at different sites should be sought in a common pathway.

Conditions in utero and cancer risk

There is increasing recognition that conditions in utero are of importance for later cancer risk in several organs, particularly the testis and breast. A review of the most recent literature on this topic is therefore warranted. The PubMed database was searched for relevant recent literature on intrauterine conditions associated with cancer risk later in life, with particular emphasis on the testis, breast, but also studies pertaining to other organs were included. Epidemiological and experimental data support the hypothesis that factors acting in utero play a role in the development of cancer in the testis and breast. For other organs, such as the prostate, urinary system and colorectum, the results are inconclusive. While conditions during foetal life are associated with later cancer risk in the testis and breast, the biological mechanisms are for the most part elusive. They are, however, likely to involve hormonal disturbances, number of cells at risk, and genetic or epigenetic events.