Hormone replacement therapy and screening mammography: analysis of the results in the Bouches du Rhône programme

Estimation of the benefit and harms of including clinical breast examination in an organized breast screening program

BACKGROUND

There is controversy about the value of clinical breast examination (CBE) in addition to mammography for breast screening. The study investigates the associations between risk factors such as mammographic density, hormone therapy use and family history and the effectiveness of screening mammography with or without CBE.

METHODS

The cohort consists of women 50-69 years old screened at the Ontario Breast Screening Program. The associations of the risk factors were investigated using a joint logistic regression model that accommodates the partially unobserved disease status, clustered data structures, individual risk factors, and the dependence between true and false detection.

RESULTS

Having high mammographic density, a first degree relative with breast cancer and using hormone therapy generally increased a woman's probability of being referred correctly. For low risk group (defined as without dense breasts, family history, and not currently using hormone therapy), the average loss of specificity ranged from 3.6% to 5.7% and the gain of sensitivity was between 10.6% and 21.2% with the addition of CBE.

CONCLUSIONS

The addition of CBE to mammography would increase the overall sensitivity and decrease the specificity. CBE can be targeted to those women in which it has the highest net benefit.

Effect of start age of breast cancer screening mammography on the risk of false-positive results

OBJECTIVE

To estimate the false-positive (FP) risk according to the start age of mammography screening (45-46 or 50-51 years).

METHOD

Data from eight regions of the Spanish breast cancer screening programme from 1990 to 2006 were included (1,565,364 women). Discrete time-hazard models were used to ascertain the effect of age and time-related, programme-related and personal variables on FP leading to any further procedure and to invasive procedures (FPI). In a subset we estimated the differential FP risk of starting screening at 45-46 years (175,656 women) or 50-51 (251,275).

RESULTS

A start age of 45-46 versus 50-51 years increased both FP (OR=1.20; 95%CI: 1.13-1.26) and FPI risks (OR=1.43 (95%CI: 1.18-1.73).Other factors increasing FP risk were premenopausal status (FP OR=1.26; 95%CI: 1.23-1.29 and FPI OR=1.22; 95%CI: 1.13-1.31), prior invasive procedures (FP OR=1.52; 95%CI: 1.47-1.57 and FPI (OR=2.08; 95%CI: 1.89-2.28) and family history (FP OR=1.16; 95%CI: 1.12-1.20 and FPI OR=1.26; 95%CI: 1.13-1.41). FP risk was increased by double reading (OR=1.36; 95%CI: 1.23-1.51) and FPI risk by double views (OR=1.34; 95%CI: 1.18-1.52). Both the cumulative FP and FPI risks were higher in women commencing screening at 45-46 years versus 50-51 years (33.30% versus 20.39% and 2.68% versus 1.76%).

CONCLUSIONS

Starting screening earlier increases the cumulative risk of FP and FPI.

Type of hormone therapy and risk of misclassification at mammography screening

OBJECTIVE

Current users of hormone therapy (HT) are known to have a lower accuracy of mammography screening than do never users. We studied whether the risk of misclassification depends on type of hormone, administration, regimen, and dose of the therapy.

METHODS

We linked data from mammography screening registers with drug prescription registers from Fyn, Denmark to identify current and never HT users among screening participants. We compared false-positive risks and interval cancer proportions between current users of different HT preparations, taking women's age, breast density, screen number, and age of comparison mammogram into account.

RESULTS

Estrogen therapy users had a significantly higher false-positive risk when the administration was by injection instead of oral (relative risk [RR], 2.37; 95% CI, 1.37-4.09). Women using sequential estrogen plus progestogen therapy had a significantly higher false-positive risk (RR, 1.94; 95% CI, 1.16-3.26) and a nonsignificantly higher interval cancer proportion (RR, 4.29; 95% CI, 0.69-26.53) when the administration of both hormones was transdermal instead of oral. Using tibolone instead of comparable hormones gave a nonsignificantly lower false-positive risk and a nonsignificantly higher interval cancer proportion.

CONCLUSIONS

Our data showed increased risks of misclassification at mammography screening among women using estrogen injections or transdermal, sequential estrogen plus progestogen. Tibolone seems to offer no advantage regarding accuracy of screening mammography.

[Assessment of the dense breast within the French screening program: the role of ultrasonography]

Mammographic density is associated with an increased risk of breast cancer. It also reduces the reliability of screening mammography. Among the population targeted by the French screening program, about 28% have dense breasts and 3% have very dense breasts. Breast density varies with age, HRT and mammographic technique. Ultrasonography for dense but otherwise clinically and mammographically normal breasts allows detection of cancers not visible on mammograms. The French program protocol allows the evaluation of results from breast US in this context with regards to the number of detected cancers and false positive rate.

The influence of HRT on technical recall in the UK Breast Screening Programme: are pain, compression force, and compressed breast thickness contributing factors?

AIM

To investigate recall for technical reasons within the UK Breast Screening Programme, and to determine whether differences exist in those women using hormone replacement therapy (HRT), considering potential associations with reported pain, compression force used and compressed breast thickness (CBT) obtained.

MATERIALS AND METHOD

A prospective cohort study of 2765 women attending for incident round breast screening appointments who were either HRT users, with a minimum of 1 year duration (n=1077), or had never used HRT (n=1688). Data were collected using technical recall records, a radiographer data-collection sheet, and a self-administered participant questionnaire.

RESULTS

Sixty-eight (2.5%) participants were recalled for technical reasons of whom 28 (2.6%) were HRT and 40 (2.4%) non-HRT users. This difference was not statistically significant (p=0.80). Significant differences were found for CBT between those HRT users who were and were not recalled for technical reasons (p<0.01) and for the similar categories of non-HRT users (p=0.03). No significant differences were found for force between those HRT users who were recalled or not (p=0.73) and for the similar categories of non-HRT users (p=0.07). Similarly no significant differences were found for pain between those HRT users who were recalled or not (p=0.75) and for the similar categories of non-HRT users (p=0.73).

CONCLUSION

CBT was the only variable to have both a statistically and a clinically significant relationship with technical recall.

Influence of Patterns of Hormone Replacement Therapy Use and Mammographic Density on Breast Cancer Detection

BACKGROUND

There is evidence that factors such as current hormone replacement therapy (HRT) use and mammographic density may each lower the sensitivity of mammography and are associated with a greater risk of developing an interval cancer. This study explores this relationship further by examining the influence of patterns of HRT use and the percentage of mammographic density on the detection of breast cancer by classification of interval cancer.

METHODS

This study uses a case-case design nested within a cohort of women screened by the Ontario Breast Screening Program between 1994 and 2002. Interval cancers, both those missed at screening but seen on retrospective review (n = 87) or true intervals without visible tumor signs at screening (n = 288) were matched to 450 screen-detected cancers. The association between the percentage of mammographic density, measured by radiologists and a computer-assisted method, and HRT use, ascertained from a mailed questionnaire, and the risk of being diagnosed with an interval cancer was estimated using conditional logistic regression.

RESULTS

A monotonic gradient of increasing risk for interval cancers was found for each 25% increase in mammographic density [odds ratio (OR), 1.77; 95% confidence intervals (95% CI), 1.07-2.95 for missed intervals and OR, 2.16; 95% CI, 1.59-2.94 for true intervals]. After adjusting for mammographic density, a significantly increased risk for true-interval cancers remained for women taking estrogen alone (OR, 1.75; 95% CI, 1.11-2.83) as well as for missed- (OR, 2.84; 95% CI, 1.32-6.13) and true-interval cancers (OR, 1.79; 95% CI, 1.10-2.90) for women taking combined HRT.

CONCLUSIONS

Information on mammographic density and HRT use should routinely be collected at the time of screening. Women at risk should be made aware of the lower sensitivity of mammography and offered alternative procedures for screening.

Determinants of false positive recall in an Australian mammographic screening program

We conducted a case-control study (n=30128) to assess the importance of clinical (e.g., family history, age, hormone replacement therapy (HRT) use and duration) and service-related characteristics (e.g., time since introduction of Kodak MINR2000 film, year of screen) for false positive (FP) recall at BreastScreen Victoria, Australia. There was an age-adjusted upward trend in FP recall rates with year of screen at first (odds ratio (OR) 1.11, 95% confidence interval (95% CI) 1.08-1.13) and subsequent rounds (OR 1.04, 95% CI 1.01-1.06). In the multivariate analysis, the upward trend only remained for first round and age and family history also remained statistically significant at first round. At subsequent rounds the time since introduction of MINR2000, age, strong family history of breast cancer, use of HRT, recall at previous screen and previous screen at more than 27 months were all important predictors of FP recall. The rise in FP rates with year of screen at first round screening is of concern and may require further training of radiologists to improve confidence when viewing films when there a no films for comparison.

Influence of Hormone Replacement Therapy on the Accuracy of Screening Mammography

The use of hormone replacement therapy (HRT) is currently a subject of debate because of the possibility of an increase in the incidence of breast cancer and difficulties associated with breast cancer detection. The objective of this study was to determine the influence of HRT on specificity and sensitivity in a breast cancer screening program. We found that although specificity was significantly lower in menopausal women who had ever used or were currently using HRT (93.3%) compared to HRT nonusers (94.8%) at the expense of a greater number of recalls (6.9% versus 5.6%), this difference seems to be clinically irrelevant. There were no significant differences with regard to the number of invasive procedures (2.5% in the HRT versus 2.1% in the control group). We conclude that the slight decrease in sensitivity of screening mammography in HRT users is not clinically significant in our setting, and in any case, false positives (recalled women) are diagnosed correctly with additional imaging studies without the need for invasive procedures. Most women given HRT are candidates to participate in population breast cancer screening campaigns.

Impact of hormone therapy on false-positive recall and costs among women undergoing screening mammography

OBJECTIVE

We sought to evaluate the effects of hormone therapy (HT) on false-positive (FP) recall for additional breast evaluation and costs.

DESIGN

We undertook an observational cohort study of women ages 40-80 years with 2 mammography screenings in an integrated delivery system.

MEASURES

FP recall, defined as mammograms resulting in a radiologist's recommendation for additional imaging, ultrasound, or invasive procedures among disease-free women, was compared for nonusers, initiators, discontinuers, and continuers of HT. Differences in health care costs by HT were assessed for total, primary care, specialty, laboratory, radiology, inpatient, mental health, and pharmacy.

RESULTS

There was no association between HT and FP recall among women ages 40-49 years. Among women 50 years or older, current HT users, ie, initiators and continuers, had increased odds of FP recall (odds ratio; 95% confidence interval) compared with nonusers (1.2; 1.0-1.4 for women 50-59 years; 1.8; 1.5-2.2 for women 60-69; and 1.7; 1.4-2.0 for women 70-80 years). Among women 50-59 years, the odds of FP recall were attributed to opposed HT (ie, estrogen+progestin). Increases in FP recall among HT users 60 years and older was maintained for initiators, continuers, opposed, and unopposed (estrogen only). Increases in FP recall among HT users were for imaging and ultrasound but not invasive procedures. Costs for current HT users during the 12 months after screening were not higher than nonusers, except for pharmacy and outpatient mental health.

CONCLUSION

The relationship between HT use and FP recall is greatest among older women and does not result in a differential use of invasive procedures.

Hormone replacement therapy, percent mammographic density, and sensitivity of mammography

OBJECTIVE

We examine to what extent the lower mammographic sensitivity found in hormone replacement therapy (HRT) users can be explained by any association of HRT use with higher mammographic density and more difficult to detect cancers.

METHODS

We used logistic regression to estimate the odds of a false-negative screen (a breast cancer diagnosed in the 24 months after a negative screening examination) for HRT users and to estimate, and adjust for, mammographic density (measured on a continuous scale, blinded, using a reliable, computer-assisted method), tumor characteristics (size, grade, and morphology), and potential confounders (age, symptom status, family history, and prior screening) among women ages > or =55 years who attended BreastScreen Victoria for first round screening mammography in 1994 and 1995 (1,086 breast cancers) and for subsequent round screening (471 breast cancers) in 1995 and 1996.

RESULTS

After adjusting for confounders, HRT users were more likely to have a false-negative screen [first round: odds ratio (OR), 1.99; 95% confidence interval (95% CI), 1.4-2.9; subsequent round: OR, 2.29; 95% CI, 1.4-3.8]. This effect was modestly attenuated by adjusting for mammographic density (first round: OR, 1.54; 95% CI, 1.0-2.3; subsequent round: OR, 1.97; 95% CI, 1.2-3.3). Adjusting for tumor characteristics resulted in a modest increase in the odds of a false negative at first round but had no effect at subsequent round.

CONCLUSIONS

Mammographic density only partly explains the effect of HRT on sensitivity. Further research needs to clarify whether hyperemic breast tissue changes affect cancer detectability in HRT users as well as the possibility that the quality of mammography may be poor in some HRT users.

Estimated numbers of postmenopausal women treated by hormone therapy in France

OBJECTIVES

To estimate the number of women aged 50-69 years treated by hormone therapy (HT) in France before Women's Health Initiative's (WHI) results and to evaluate the potential decrease of HT prescriptions since the publication of WHI clinical trial.

METHODS

We used data from eight computerized databases of French cohort studies providing information on HT and constituted by women aged over 50 years living in metropolitan France. From these, we used direct standardization on the French population to estimate the prevalence of HT users across 5 years age groups. Data from the National Health Insurance Agency on two time-periods November 2002-January 2003 and November 2003-January 2004 were used to evaluate the evolution of HT prescriptions since WHI's publication among women aged 50-69 years living in the Rhône-Alpes region.

RESULTS

The crude prevalence of HT users among women aged 50-69 years was 52.3% (51.8-52.8) and corresponds to a standardized prevalence of 35.7% (35.1-36.4), that is about 2.56 (2.51-2.59) million women. Standardized prevalence was the highest in 50-54 years age group then it decreased significantly across the older age groups (p<10(-6)). HT reimbursements decreased significantly between the two studied time-periods in the Rhône-Alpes region (p<10(-6)) from -14 to -45%, depending on the considered age groups (65-69 or 50-54 years).

CONCLUSIONS

Although WHI results have been criticized by French professional societies based on the fact that treatments used were different in France--mainly transdermal estrogens--and that French postmenopausal women were at lower vascular risk than those of the WHI, the release of this study had effect on the prescription before the French regulatory agency (AFSSAPS) edited limiting recommendations for HT prescription. Further efforts have to be made to collect systematically information on preventive treatments used at menopause followed by evaluation studies.

Breast cancer risk in relation to different types of hormone replacement therapy in the E3N-EPIC cohort

Most epidemiological studies have shown an increase in breast cancer risk related to hormone replacement therapy (HRT) use. A recent large cohort study showed effects of similar magnitude for different types of progestogens and for different routes of administration of estrogens evaluated. Further investigation of these issues is of importance. We assessed the risk of breast cancer associated with HRT use in 54,548 postmenopausal women who had never taken any HRT 1 year before entering the E3N-EPIC cohort study (mean age at inclusion: 52.8 years); 948 primary invasive breast cancers were diagnosed during follow-up (mean duration: 5.8 years). Data were analyzed using multivariate Cox proportional hazards models. In this cohort where the mean duration of HRT use was 2.8 years, an increased risk in HRT users compared to nonusers was found (relative risk (RR) 1.2 [95% confidence interval 1.1-1.4]). The RR was 1.1 [0.8-1.6] for estrogens used alone and 1.3 [1.1-1.5] when used in combination with oral progestogens. The risk was significantly greater (p <0.001) with HRT containing synthetic progestins than with HRT containing micronized progesterone, the RRs being 1.4 [1.2-1.7] and 0.9 [0.7-1.2], respectively. When combined with synthetic progestins, both oral and transdermal/percutaneous estrogens use were associated with a significantly increased risk; for transdermal/percutaneous estrogens, this was the case even when exposure was less than 2 years. Our results suggest that, when combined with synthetic progestins, even short-term use of estrogens may increase breast cancer risk. Micronized progesterone may be preferred to synthetic progestins in short-term HRT. This finding needs further investigation.

Le dépistage organisé des cancers du sein : particularités du système français

The breast cancer screening program developed in France is an original model, adapted to the specific features of the French healthcare system. Both public and private mammographic units are involved with an active participation of practitioners in prescription and management. Two views per breast every two years together with physical examination are performed. An immediate diagnosis process is planned if an abnormality is detected. The French model is also a rigorous public health program involving prior training, strict organisation, quality assurance of all the process, double reading and epidemiologic evaluation. Logical benefits and difficulties of such a system are discussed.

Thérapeutiques hormonales de la ménopause : impact sur la densité mammographique

Whether qualitative-classified or quantitative-measured, mammographic density, which changes according to physiological variations, is nowadays commonly recognized as a factor increasing the relative risk of breast cancer. The present review aims at clarifying the impact of menopausal hormonal therapies on mammographic density. Neither Tibolone nor Raloxifene seem to have any negative impact on mammographic density. In some instances, oestrogens-progestin hormonal replacement therapies may increase mammographic density and thus reduce sensitivity and specificity of screening mammograms. Shorter intervals between mammographies combined with additional physical examination and breast ultrasonography appear to be the best way to reduce interval cancers.

Postmenopausal hormone therapy and the risk of breast cancer

Reports from the Women's Health Initiative (WHI) and the Million Women Study have indicated that postmenopausal hormone therapy increases the risk of breast cancer. At this point in time, it is not certain whether these data reflect a small increase in risk or an impact of hormone therapy on pre-existing tumors. The purpose of this review is to provide an analysis of the epidemiologic data that can help the clinician inform patients and assist patients in their decision-making.

Hormones and mammographic breast density

Mammographic density reveals information about the hormonal environment along with the heritability in which breast cancer develops. This is made possible by the widespread use of population screening by mammography. Increasingly this is an important observation not just for population studies, which reveal disease determinants, but also for the individual. Density reveals the effect of the intrinsic hormonal environment and its background genetics, and also the effect of pharmaceuticals--agents used for disease control and prevention and hormone replacement therapy (HRT) used for well-being around the menopause. Increasingly this focus on the individual will need methods of measurement of density that can be monitored with greater accuracy than the widely used BI-RADS 4 categories. For this purpose studies are under way to measure volume of dense tissue as a continuous variable. In due course, measurement of density will be used as a biomarker of risk, employed in risk models and to monitor interventions. Before this can happen more knowledge will be needed of the change occurring naturally through the menopause and the differences between individuals. This will need specific study backed up with detailed information about the patient on large numbers of women and their mammograms. Currently the widespread use of HRT has increased the prevalence of the dense patterns and potentially may adversely affect the effectiveness of mammographic screening programmes. There is a large literature recording this from which we see that combined continuous preparations of oestrogen progestin are more likely to cause increased density than oestrogen alone or tibolone. Breast density, measured more accurately, has the potential to be an important adjunct to risk estimation and to monitor interventions for breast cancer prevention with pharmaceuticals (such as SERMS) and by change in lifestyle behaviours.

Political interpretation of scientific evidence--case study of breast cancer screening policies around the world

Early detection of breast cancer has been studied for effectiveness in reducing mortality for more than four decades. During this period numerous studies took place, with more than half a million participating women. In spite of large amounts of nonconflicting data, different countries took varying lengths of time to establish a policy, and came up with a variety of policies, quite different from one another. Inherent differences between the countries in structure of the health system, in the commitment to public health activities, and in opinions and health habits of the relevant populations may explain these different outcomes.

Differential association of oral and transdermal oestrogen-replacement therapy with venous thromboembolism risk

BACKGROUND

Oral oestrogen-replacement therapy (ERT) activates blood coagulation and increases the risk of venous thromboembolism (VTE) in postmenopausal women. Transdermal ERT has little effect on haemostasis, but data assessing its effect on thrombotic process are scarce. We aimed to examine the effect of the route of oestrogen administration on VTE risk.

METHODS

We did a multicentre hospital-based case-control study of postmenopausal women in France. During 1999-2002, we recruited 155 consecutive cases with a first documented episode of idiopathic VTE (92 with pulmonary embolisms and 63 with deep venous thrombosis), and 381 controls matched for centre, age, and time of recruitment.

FINDINGS

Overall, 32 (21%) cases and 27 (7%) controls were current users of oral ERT, whereas 30 (19%) cases and 93 (24%) controls were current users of transdermal ERT. After adjustment for potential confounding variables, the odds ratio for VTE in current users of oral and transdermal ERT compared with non-users was 3.5 (95% CI 1.8-6.8) and 0.9 (0.5-1.6), respectively. Estimated risk for VTE in current users of oral ERT compared with transdermal ERT users was 4.0 (1.9-8.3).

INTERPRETATION

Oral but not transdermal ERT is associated with risk of VTE in postmenopausal women. These data suggest that transdermal ERT might be safer than oral ERT with respect to thrombotic risk.

Does hormone replacement therapy increase the frequency of breast atypical hyperplasia in postmenopausal women? Results from the Bouches du Rhone district screening campaign

It is thought that the risk of atypical hyperplasia (AH) increases with age, particularly among postmenopausal women. Three hypotheses were investigated to try to explain this phenomena: use of hormone replacement therapy (HRT), increased breast cancer screening and improvements in radiological quality. Data were collected from the Bouches du Rhône breast cancer screening programme database and from the pathological registry of all women operated on for breast diseases in the district. The AH incidence rate was studied using a Poisson regression analysis. The change in the profile of breast diseases was explored through studying changes in the proportion of AH among benign lesions and malignant diseases. The AH incidence rate significantly increased over time (13.6% per year). The proportion of AH among the benign diseases increased with time and was significantly higher for HRT users (Odds Ratio (OR)=2.05; 95% Confidence Interval (CI): 1.43-2.93). While AH decreased with age among HRT non-users, it increased among users as a proportion of both benign and malignant lesions. The AH incidence rate significantly increased among pre- and postmenopausal women. Our study suggests that this increase is partly explained by the incidental discovery of these lesions by mammography and partly by a real increase of the disease among HRT users.

Hormone replacement therapy and mammographic screening

The benefits of hormone replacement therapy (HRT) with oestrogen are well known and have led to widespread usage of HRT in post-menopausal women. There is an increased relative risk of breast cancer with prolonged HRT use of 1.7 at worst and this does not warrant more frequent screening. HRT itself makes mammographic screening less effective by adversely affecting both the sensitivity and specificity of screening mammography.A number of large studies have shown a reduction in the sensitivity of screening mammography of between 7% and 21% in current HRT users. This reduction in sensitivity is seen only in women over the age of 50 and is more marked when using single view mammography. The reduction in sensitivity is largely confined to those women who have a dense mammographic background pattern while on HRT. HRT use is also associated with a reduction in specificity of between 12% and almost 50%. This reduction in specificity is mainly found at incident screens. What can be done to minimize the adverse effects of HRT on mammographic screening? The imminent introduction of two views at all screens within the National Health Breast Screening Programme will be helpful. Short-term cessation of HRT use may deter attendance for screening by HRT users and is unproven. Combined oestrogen and progesterone preparations taken continuously appear to be particularly associated with adverse breast screening performance, while tibolone may have little effect on mammographic density. Manipulation of the type of HRT preparations used may allow the adverse effects of HRT on breast screening to be reduced.

Screening women at high risk of breast cancer on the basis of evidence

Geneticists are able to identify the risk of breast cancer. Strategies on offer include prevention, early diagnosis by screening, and prophylactic surgery. This paper analyses the evidence for offering screening. The radiation dose of mammography has been measured, but the risk is not fully known. Mammography screening of women of 40-50 years in the normal population has known effect. Little evidence is available for women under 40 years or for women with genetic susceptibility to breast cancer. Dense parenchymal pattern is associated with high grade cancers, and is both a risk factor and a reason for impaired screening sensitivity. Whether this applies to younger women or women at high risk is speculative. The pathological features of the cancers in gene carriers show differences from those occurring in normal women. This work should be correlated with imaging features. There is no literature to support the use of newer imaging methods in these women. Ultrasound and MRI avoid radiation and may be useful in dense breasts. SestaMIBI and PET scanning are not yet mature enough for screening, and may never have such a role. Any newer modality must be subjected to a formal randomised trial before being offered to screen women at high risk.

Hormone replacement therapy and accuracy of mammographic screening

BACKGROUND

Hormone replacement therapy (HRT) is commonly used and may affect the accuracy of mammographic screening.

METHODS

We examined the sensitivity, specificity, and small-cancer detection rate according to HRT use in 103,770 women in Victoria, Australia, who attended first-round screening in 1994 and who did not have a personal history of breast cancer or a breast lump or a bloodstained or watery nipple discharge at the time of screening. BreastScreen Victoria provides mammography to women aged 40 years and older every 2 years. Unconditional logistic modelling was used to adjust for age, family history, and symptom status.

FINDINGS

The sensitivity of screening mammography for a 2-year screening interval was lower in HRT users (64.8% [95% CI 58-72]) than non-users (77.3% [74-81]). In the target group (50-69 years), the sensitivity was 64.3% (57-72) in HRT users and 79.8% (76-84) in non-users. Among women who were diagnosed with cancer during the 2-year screening interval, HRT users were more likely to have a false negative result than non-users (odds ratio 1.60 [1.04-2.21]) after adjusting for potential confounding factors. Specificity was 0.6% lower in HRT users compared with non-users. Among women who did not have cancer diagnosed in the interval, HRT users were more likely to have a false positive result (adjusted odds ratio 1.12 [1.05-1.19]).

INTERPRETATION

We show that HRT use reduces the sensitivity of mammographic screening. In countries where HRT use is widespread, the reduction in sensitivity with HRT use may undermine the capacity of population-based mammographic-screening programmes to realise their potential mortality benefit.