Benign proliferative epithelial disorders of the breast: a review of the epidemiologic evidence

Best acupuncture method for mammary gland hyperplasia: Evaluation of randomized controlled trials and Bayesian network meta-analysis

Objective

To evaluate the effectiveness of different acupuncture treatments for mammary gland hyperplasia (MGH) using a network meta-analysis.

Methods

Several databases were searched without language restrictions from 2000 to February 2023, including PubMed, Embase, Web of Science, Cochrane Library, China Science and Technology Journal Database, China Biology Medicine Database, Wanfang Database, China National Knowledge Infrastructure Database, and other professional websites and gray literature. Inclusion criteria were adult women diagnosed with MGH; intervention measures included acupuncture and related therapies; the control group was treated with simple drugs; and the research type was a randomized controlled trial (RCT). The primary outcomes were treatment effectiveness and estradiol and progesterone levels. Secondary outcomes were breast lump size and visual analog scale (VAS) score of breast pain. Exclusion criteria were studies unrelated to MGH, incorrect study populations, control measures or interventions, incomplete data, non-RCTs, case reports, and animal experiments. Cochrane tools were used to assess the risk of bias. The R software (x64 version 4.2.1), Review Manager 5.3 software and STATA 16.0 software were used for data analysis.

Results

Following a rigorous screening process, data extraction, and quality assessment, 48 eligible RCTs encompassing 4,500 patients with MGH and 16 interventions were included. The results indicated that acupuncture, alone or in combination with traditional Chinese or Western medicine, had better therapeutic effects than conventional therapy. In terms of effectiveness, warm needle acupuncture was the best choice (94.6%). Bloodletting pricking was the most effective method (85.7%) for lowering progesterone levels. Bloodletting pricking was the most effective method (98.3%) for lowering estradiol levels. Manual acupuncture combined with traditional Chinese medicine was the most effective (74.5%) treatment to improve the size of the breast lump. Warm needle acupuncture was the most effective (69.8%) in improving the VAS score.

Conclusion

Acupuncture therapy was more effective in treating MGH than drug therapy alone, and warm needle acupuncture and bloodletting pricking were the two best options. However, larger sample sizes and high-quality RCTs are required.

Investigating the Link between Early Life and Breast Anomalies

Several factors during childhood and adolescence are thought to be associated with the development of proliferative benign breast diseases and breast cancer in adulthood. In order to identify them, the authors conducted an extensive review of the literature up to October 2022, searching for clinical studies, reports, and guidelines in English. A thorough Medline/Pubmed and Google scholar database research was performed, investigating the link between diet, exercise, age of menarche, body mass index, ionizing radiation exposure during childhood and adolescence, and proliferative breast diseases and breast cancer in adulthood. A list of keywords, including breast disorders, adolescence, childhood, and breast cancer was included in our search algorithm. Numerous studies concede that the development of breast disease in adulthood is influenced by various risk factors, whose influence begins during early childhood and adolescence.

Factors associated with breast disorders detected by clinical breast examination during pregnancy and six months postpartum in Ibadan, South-western Nigeria

Background

Breast disorders (BD) during pregnancy and postpartum cause anxiety and reduce women's quality of life. The study examined BD risk factors during pregnancy and six months after delivery.

Methods

Women attending antenatal clinics at 26 weeks gestation were recruited. 1248 pregnant women were followed six months postpartum. During recruitment, a validated questionnaire was used to collect participant characteristics and risk factors. Palpable lumps, inflammation, persistent pain, and abnormal nipple discharge were classified breast disorders. Statistical analysis used multiple logistic and cox regression models at p<0.05.

Results

Women with benign breast disease were more likely to develop BD (aOR = 2.63, 95% CI = 1.50-4.88). One pregnancy increases the risk of BD more than three times (aOR=0.52, 95%CI: 0.29-0.95). History of breast trauma (aHR=3.59, 95%CI: 1.40-9.17) and 3 miscarriages vs. none (aHR=2.23, 95%CI: 1.04-4.23) were also risk factors for BD. The second quartile of physical activity was associated with a lower risk of BD (aHR=0.35, 95%CI: 0.15-0.78).

Conclusion

Women with breast trauma and miscarriage are more likely to develop breast disorders during pregnancy and six months after delivery. Our findings highlight the need for additional longitudinal research to validate these findings and plans for prevention and control. Keywords: Breast disorders, pregnancy, postpartum, predictors, longitudinal study.

The relationship between using estrogen and/or progesterone and the risk of mammary gland hyperplasia in women: a meta-analysis

BACKGROUND

As reported that the usage of estrogen and/or progesterone increases the risk of mammary gland hyperplasia (MGH) with conflicting results. Therefore, we conducted a meta-analysis to higher elucidate the relationship between hormones and MGH.

METHOD

PubMed, Embase, Web of Science, Cochrane Library, Chinese National Knowledge Infrastructure, and Wan-fang database were searched for studies until April 28, 2021.

RESULTS

Nine related studies were included in the present meta-analysis. We found that the usage of estrogen and/or progesterone had a significant association with increasing the risk of MGH (RR = 1.56, 95% CI: 1.13-2.15, p = .000). The subgroup results showed that the risk of MGH increased in the Mix population (RR = 1.72, CI: 1.58-1.88, p < .001) but no significant difference in the Asian population. Meanwhile, as for using estrogen plus progesterone (EPP) and postmenopausal women the risk of MGH, respectively, increased (RR = 1.74, CI: 1.22-2.47, p = .002) and (RR = 1.75, CI: 1.24-2.47, p = .001) but no significant different for using estrogen alone and premenopausal women.

CONCLUSIONS

This study findings indicated that using estrogen and/or progesterone might increase the risk of MGH in premenopausal and postmenopausal women.

Physical activity and risk of benign proliferative epithelial disorders of the breast, in the Women's Health Initiative

BACKGROUND

Recreational physical activity (PA) has been shown to be inversely associated with breast cancer risk. However, the association of recreational PA with benign proliferative epithelial disorders (BPED) of the breast, conditions associated with increased risk of breast cancer, has not been adequately studied.

METHODS

We used data from an ancillary study of benign breast disease conducted among the 68 132 postmenopausal women (aged 50-79 at recruitment) participating in the Women's Health Initiative randomized clinical trials. All clinical trial participants underwent annual or biennial mammogram screening. During the follow-up, for women who reported breast biopsies but were cancer free, the associated histological sections were obtained and subjected to standardized central pathology review. Self-reported recreational PA at baseline (n = 61 684) and at 3 years of the follow-up (n = 55 923) were quantified as metabolic equivalents [MET]-h/week. There were 1624 confirmed BPED cases during an average follow-up time of 7.7 years. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Higher average PA over 4 years was associated with lower risk of non-atypical BPED (P-trend = 0.02). There was a 6% lower risk of non-atypical BPED for every 5 MET-h/week increase between baseline and year 3 (HR = 0.94, 95% CI 0.89-0.99). Compared with women who remained inactive (PAbaseline and PAyear3 <9 MET-h/week), those who became active (PAbaseline<9 MET-h/week to PAyear3 ≥9 MET-h/weekee), remained active (PAbaseline and PAyear3 ≥9 MET-h/week), or decreased activity (PAbaseline ≥9 MET-h/week to PAyear3 <9 MET-h/week) had lower BPED risk.

CONCLUSIONS

Recreational physical activity after menopause was associated with lower BPED risk among postmenopausal women.

Atypical Ductal Hyperplasia after Vacuum-Assisted Breast Biopsy: Can We Reduce the Upgrade to Breast Cancer to an Acceptable Rate?

(1) Background: to evaluate which factors can reduce the upgrade rate of atypical ductal hyperplasia (ADH) to in situ or invasive carcinoma in patients who underwent vacuum-assisted breast biopsy (VABB) and subsequent surgical excision. (2) Methods: 2955 VABBs were reviewed; 141 patients with a diagnosis of ADH were selected for subsequent surgical excision. The association between patients’ characteristics and the upgrade rate to breast cancer was evaluated in both univariate and multivariate analyses. (3) Results: the upgrade rates to ductal carcinoma in situ (DCIS) and invasive carcinoma (IC) were, respectively, 29.1% and 7.8%. The pooled upgrade rate to DCIS or IC was statistically lower at univariate analysis, considering the following parameters: complete removal of the lesion (p-value < 0.001); BIRADS ≤ 4a (p-value < 0.001); size of the lesion ≤15 mm (p-value: 0.002); age of the patients <50 years (p-value: 0.035). (4) Conclusions: the overall upgrade rate of ADH to DCIS or IC is high and, as already known, surgery should be recommended. However, ADH cases should always be discussed in multidisciplinary meetings: some parameters appear to be related to a lower upgrade rate. Patients presenting these parameters could be strictly followed up to avoid overtreatment.

MYLK and PTGS1 Genetic Variations Associated with Osteoporosis and Benign Breast Tumors in Korean Women

Osteoporosis, characterized by reduced bone mass and increased bone fragility, is a disease prevalent in women. Likewise, breast cancer is a multifactorial disease and considered the major cause of mortality in premenopausal and postmenopausal women worldwide. Our data demonstrated the association of the MYLK gene and PTGS1 gene variants with osteoporosis and benign breast tumor risk and the impact of ovariectomy on osteoporosis in Korean women. We performed a genome-wide association study (GWAS) of women with osteoporosis and benign breast tumors. There were 60 single nucleotide polymorphisms (SNPs) and 12 SNPs in the MYLK and PTGS1 genes, associated with benign breast tumors and osteoporosis. Our study showed that women with homozygous MYLK rs12163585 major alleles had an increased risk of osteoporosis following ovariectomy compared to those with minor alleles. Women carrying the minor PTGS1 rs1213265 allele and not treated via ovariectomy carried a higher risk of osteoporosis than those who underwent ovariectomy with a homozygous genotype at the major alleles. Our results suggest that both the MYLK and PTGS1 genes are genetic factors associated with the phenotypes, and these associations appear to be modulated by ovariectomy.

Family History, Reproductive, and Lifestyle Risk Factors for Fibroadenoma and Breast Cancer

Background

To understand which breast cancer (BC) risk factors also increase the risk of fibroadenoma and investigate whether these factors have the same effect in BC patients with previous fibroadenoma.

Methods

Using multistate survival analysis on a large dataset (n = 58 322), we examined the effects of BC risk factors on transitions between three states: event-free, biopsy-confirmed fibroadenoma, and BC. Hazard ratios and corresponding 95% confidence intervals associated with covariate effects were estimated. Median follow-up time was 25.3 years.

Results

The mean ages at diagnosis of fibroadenoma and BC were 42.6 and 48.3 years, respectively. Participant characteristics known to increase the risk of BC were found to increase the risk of fibroadenoma (family history of BC and higher education). Participant characteristics known to confer protective effects for BC (older age at menarche, more children, and larger childhood body size) were found to reduce fibroadenoma risk. The effect sizes associated with the direct transitions from event-free to fibroadenoma and BC were generally not different for the covariates tested. Age at fibroadenoma diagnosis was associated with the transition from fibroadenoma to BC (hazard ratio_{per year increase} = 1.07 [95% confidence interval = 1.03 to 1.12]).

Conclusion

We showed that biopsy-confirmed fibroadenomas shared many risk factors with BC. More work is needed to understand the relationships between fibroadenoma and BC to identify women who are at high risk of developing BC after a fibroadenoma diagnosis.

Atypical ductal hyperplasia: Our experience in the management and long term clinical follow-up in 71 patients

INTRODUCTION

Atypical ductal hyperplasia (ADH) is a high-risk benign lesion found in approximately 1-10% of breast biopsies and associated with a variable incidence of carcinoma after surgical excision. The main goal of our study is to present our experience in the management and long-term follow-up of 71 patients with ADH diagnosed on breast biopsy.

MATERIALS AND METHODS

Results of 3808 breast biopsy specimens from 1 January 2000 to 31 December 2005 were analyzed to identify all biopsies which resulted in a diagnosis of ADH. The histopathological results of the 45 patients who underwent surgery were analyzed. Long-term follow-up for the remaining patients was carried out.

RESULTS

45 of 71 (63.4%) patients with histological diagnosis of ADH on breast biopsy underwent surgery. Definitive histological results revealed invasive carcinoma in 7 cases (15.6%), high grade Ductal Carcinoma in situ (DCIS) in 10 (22.2%) patients, Lobular Carcinoma in situ (LCIS) in 4 cases (8.9%) and benign findings in 24 cases (53.3%). 12 of 71 (16.9%) patients underwent only long term follow-up; one (8,3%) of these developed invasive breast carcinoma after 6 years.

CONCLUSION

Atypical ductal hyperplasia diagnosed on breast biopsy is associated with a relatively high incidence of invasive carcinoma and high grade ductal carcinoma in situ at the time of surgical excision. Certain radiological and cytological criteria can be used to help determine which patients should forgo surgery and be followed up with good results. Long term follow-up is always crucial for patients who have not undergone surgery.

A MOUSE MODEL OF MAMMARY HYPERPLASIA INDUCED BY ORAL HORMONE ADMINISTRATION

Background:

Mammary hyperplasia is one of the most common benign breast disorders. Although traditional Chinese medicine has a vast experience in the treatment of mammary hyperplasia, it is not accepted widely due to its unclear mechanism.

Methods and Materials:

To address the mechanism, we developed a mouse model of mammary hyperplasia. We gave mice estradiol valerate tablets and progesterone capsules sequentially for one month by intragastric administration.

Results:

Mice treated by this method had a series of pathological changes which are similar to those detected in women with mammary hyperplasia, including ectopic level of estradiol and progesterone in serum, hyperplasia of mammary glands and increased expression of ERα and PR.

Conclusion:

This model will facilitate the mechanical study of traditional medicine on mammary hyperplasia.

Serum IGFBP-2 and Risk of Atypical Hyperplasia of the Breast

Atypical hyperplasia of the breast (AH) is associated with increased risk of subsequent invasive breast cancer, yet little is known about the etiology of AH. Insulin-like growth factor binding protein 2 (IGFBP-2) may contribute to the development of AH due to its proliferative effects on mammary tissue. We conducted a nested case-control study of postmenopausal women enrolled in Women's Health Initiative-Clinical Trial. Cases were 275 women who developed incident AH during follow-up, individually (1 : 1) matched to controls. Levels of IGFBP-2 were determined from fasting serum collected at baseline. Multivariable conditional logistic regression models were used to estimate odds ratios for the association of IGFBP-2 with risk of AH. Serum IGFBP-2 was associated with a nonsignificant decrease in risk for AH, when comparing the highest quartile to lowest quartile (OR = 0.65; 95% CI = 0.32–1.31). This decrease in risk was most evident when analyses were restricted to nondiabetic, nonusers of hormone therapy (OR = 0.33, 95% CI = 0.13–0.86, p_trend = 0.06) and nondiabetic women who were overweight or obese (OR = 0.43, 95% CI = 0.18–1.03, p_trend = 0.05). Results from this study provide some support for an inverse association between serum IGFBP2 levels and risk of AH, particularly in nondiabetic women who are overweight or obese. Further studies are required to confirm these results.

The role of general nuclear medicine in breast cancer

The rising incidence of breast cancer worldwide has prompted many improvements to current care. Routine nuclear medicine is a major contributor to a full gamut of clinical studies such as early lesion detection and stratification; guiding, monitoring, and predicting response to therapy; and monitoring progression, recurrence or metastases. Developments in instrumentation such as the high-resolution dedicated breast device coupled with the diagnostic versatility of conventional cameras have reinserted nuclear medicine as a valuable tool in the broader clinical setting. This review outlines the role of general nuclear medicine, concluding that targeted radiopharmaceuticals and versatile instrumentation position nuclear medicine as a powerful modality for patients with breast cancer.

Breast cancer risk associated with benign breast disease: systematic review and meta-analysis

Benign breast disease (BBD) is a broad category of diagnoses reported to convey a variable degree of increased risk of developing breast cancer. A meta-analysis of the existing literature was performed to quantify the risk estimate associated with BBD. Pubmed, Google Scholar, and EMBASE databases were searched in January 2011. English retrospective and prospective observational studies published from 1972 to 2010 evaluating BBD and the risk of breast cancer were included with data acquisition reported from 1930 to 2007. Eligibility was performed independently following a standardized protocol for full-text publication review by a single reviewer and reviewed by a second author. Of the 3,409 articles retrieved from the literature search, 32 studies met the selection criteria. Reported risk estimates, including relative risk, odds ratio, standardized incidence ratios, rate ratio, hazards ratio, and incidence rate ratio, were the primary outcomes extracted. The most commonly reported pathologies were decided prior to extraction and organized into the following categories for analysis of the extracted risk estimate: non-proliferative disease (NPD), proliferative disease without atypia, benign breast disease not otherwise specified (BBD), and atypical hyperplasia not otherwise specified (AHNOS). The mean age at benign breast biopsy was 46.1 years and the mean age of developing breast cancer was 55.9 years. The mean follow-up length was 12.8 years (range 3.3-20.6). The summary risk estimate of developing breast cancer for NPD was 1.17 (N = 8; 95% CI 0.94-1.47). Proliferative disease without atypia was associated with significantly increased risk of future breast cancer, summary relative risk 1.76 (N = 15; 95% CI 1.58-1.95). The summary risk estimate for AHNOS was 3.93 (N = 13; 95% CI 3.24-4.76). This meta-analysis demonstrates that proliferative benign breast disease with or without atypia is associated with a significant increase in risk of developing breast cancer. These data support management strategies for women with benign breast disease such as additional screening methods or chemoprevention.

Breast cancer risk accumulation starts early: prevention must also

Nearly one in four breast cancers is diagnosed before the age of 50, and many early-stage premalignant lesions are present but not yet diagnosed. Therefore, we review evidence to support the strategy that breast cancer prevention efforts must begin early in life. This study follows the literature review methods and format. Exposures during childhood and adolescence affect a woman's long-term risk of breast cancer, but have received far less research attention than exposures that occur later in life. Breast tissue undergoes rapid cellular proliferation between menarche and first full-term pregnancy, and risk accumulates rapidly until the terminal differentiation that accompanies first pregnancy. Evidence on childhood diet and growth in height, and adolescent alcohol intake, among other adolescent factors is related to breast cancer risk and risk of premalignant proliferative benign lesions. Breast cancer prevention efforts will have the greatest effect when initiated at an early age and continued over a lifetime. Gaps in knowledge are identified and deserve increase attention to inform prevention.

Insulin, estrogen, inflammatory markers, and risk of benign proliferative breast disease

Women with benign proliferative breast disease (BPBD) are at increased risk for developing breast cancer. Evidence suggests that accumulation of adipose tissue can influence breast cancer development via hyperinsulinemia, increased estrogen, and/or inflammation. However, there are limited data investigating these pathways with respect to risk of BPBD. We evaluated serologic markers from these pathways in a case-control study of postmenopausal women nested within the Women's Health Initiative Clinical Trial. Cases were the 667 women who developed BPBD during follow-up, and they were matched to 1,321 controls. Levels of insulin, estradiol, C-reactive protein (CRP), and adiponectin were measured in fasting serum collected at baseline. Conditional logistic regression models were used to estimate ORs for the association of each factor with BPBD risk. Among nonusers of hormone therapy, fasting serum insulin was associated with a statistically significant increase in risk of BPBD (OR for highest vs. lowest quartile = 1.80; 95% confidence interval, CI, 1.16-2.79; Ptrend = 0.003) as were levels of estradiol (OR for highest vs. lowest tertile = 1.89; 95% CI, 1.26-2.83; Ptrend = 0.02) and CRP (OR for highest vs. lowest quartile = 2.46; 95% CI, 1.59-3.80; Ptrend < 0.001). Baseline adiponectin level was inversely associated with BPBD risk (OR for highest vs. lowest quartile = 0.47; 95% CI, 0.31-0.71; Ptrend < 0.001). These associations persisted after mutual adjustment, but were not observed among users of either estrogen alone or of estrogen plus progestin hormone therapy. Our results indicate that serum levels of estrogen, insulin, CRP, and adiponectin are independent risk factors for BPBD and suggest that the estrogen, insulin, and inflammation pathways are associated with the early stages of breast cancer development.

Preadolescent and adolescent risk factors for benign breast disease

PURPOSE

It is well established that exposures during childhood and adolescence affect breast cancer risk much later in life. Recently, studies have begun to evaluate whether early life exposures might also impact the risk of developing benign breast disease (BBD). A diagnosis of proliferative BBD independent of other breast cancer risk factors also increases the subsequent risk of breast cancer; therefore, understanding how to decrease the incidence of BBD may have important implications for primary breast cancer prevention.

METHODS

We reviewed several studies from prospective cohort studies that have investigated the relationship between risk factors during childhood and adolescence, such as anthropometric and reproductive characteristics as well as diet and other behaviors, and subsequent risk of BBD.

RESULTS

Higher intake of vegetable oils, nuts, vitamin E, and fiber and lower consumption of animal fat, red meat, and alcohol are associated with reduced risk of BBD. Childhood weight and adolescent body mass index are inversely associated with BBD risk, whereas a greater peak height velocity during adolescence is associated with a higher risk of BBD. There was no association between age of menarche and risk of BBD.

CONCLUSION

Early life exposures and behaviors appear to impact BBD risk. The current body of evidence further supports the importance of a life-course approach to breast cancer prevention.

Hsa-miR-375 is differentially expressed during breast lobular neoplasia and promotes loss of mammary acinar polarity

Invasive lobular carcinoma (ILC) of the breast, characterized by loss of E-cadherin expression, accounts for 5-15% of invasive breast cancers and it is believed to arise via a linear histological progression. Genomic studies have identified a clonal relationship between ILC and concurrent lobular carcinoma in situ (LCIS) lesions, suggesting that LCIS may be a precursor lesion. It has been shown that an LCIS diagnosis confers a 15-20% risk of progression to ILC over a lifetime. Currently no molecular test or markers can identify LCIS lesions likely to progress to ILC. Since microRNA (miRNA) expression changes have been detected in a number of other cancer types, we explored whether their dysregulation might be detected during progression from LCIS to ILC. Using the Illumina miRNA profiling platform, designed for simultaneous analysis of 470 mature miRNAs, we analysed the profiles of archived normal breast epithelium, LCIS lesions found alone, LCIS lesions concurrent with ILC, and the concurrent ILCs as a model of linear histological progression towards ILC. We identified two sets of differentially expressed miRNAs, the first set highly expressed in normal epithelium, including hsa-miR-224, -139, -10b, -450, 140, and -365, and the second set up-regulated during lobular neoplasia progression, including hsa-miR-375, -203, -425-5p, -183, -565, and -182. Using quantitative RT-PCR, we validated a trend of increasing expression for hsa-miR-375, hsa-miR-182, and hsa-miR-183 correlating with ILC progression. As we detected increased expression of hsa-miR-375 in LCIS lesions synchronous with ILC, we sought to determine whether hsa-miR-375 might induce phenotypes reminiscent of lobular neoplasia by expressing it in the MCF-10A 3D culture model of mammary acinar morphogenesis. Increased expression of hsa-miR-375 resulted in loss of cellular organization and acquisition of a hyperplastic phenotype. These data suggest that dysregulated miRNA expression contributes to lobular neoplastic progression.

Effects of short-term estrogen treatment on the progression of N-methyl-N-nitrosourea-induced premalignant mammary lesions in female Lewis rats

We studied the effects of short-term estrogen treatment (STET) on the progression of mammary lesions from ductal hyperplasia (DH) through ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) in the N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinogenesis model. Three-week-old female Lewis rats (n = 40) received an intraperitoneal injection of MNU (50 mg/kg). Three weeks later, a 3-week-release, 0.25-mg, 17β-estradiol pellet was subcutaneously implanted for 2 weeks in 20 rats (STET); the remaining 20 rats did not receive the estradiol pellets (age-matched control). All rats were killed at 12 weeks of age, and their abdominal-inguinal mammary glands were histologically examined. The incidence and multiplicity of DHs were similar between groups (STET, 90% and 3.9 ± 0.6 vs. age-matched controls, 80% and 3.0 ± 0.5). However, DCIS and IDC did not develop in STET rats, whereas DCIS (25% and 1.4 ± 0.2) and IDC (35% and 1.4 ± 0.3) developed in the age-matched controls. Immunoscores of estrogen and progesterone receptors and positive rate of proliferative cell nuclear antigen (PCNA) in DH were similar in both groups, while the positive rate of cyclin D1 was significantly reduced in the STET group (P < 0.05). Thus, STET blocked the progression from DH to DCIS in MNU-induced mammary carcinogenesis, and decreased expression of cyclin D1 may play an important role in the blockade of cell transition from DH to DCIS.

Mutations in the mitochondrial DNA D-loop region and breast cancer risk

Mitochondrial genome alterations have been suggested to play an important role in carcinogenesis. The D-loop region of mitochondrial DNA (mtDNA) contains essential transcription and replication elements, and mutations in this region may serve as a potential sensor for cellular DNA damage and a marker for cancer development. Using data and samples from the Shanghai Breast Cancer Study, we investigated MnlI restriction sites located between nucleotides 16,106 and 16,437 of the mtDNA D-loop region to evaluate restriction fragment length polymorphism (RFLP) patterns in tumor tissue from 501 primary breast cancer patients when compared with tumor tissue from 203 women with benign breast disease (BBD). RFLP patterns in correspondingly paired, adjacent, non-tumor tissues taken from 120 primary breast cancer patients and 59 BBD controls were also evaluated. Five common RFLP patterns were observed, and no significant differences were observed in the distribution of these patterns between tumor and adjacent non-tumor tissue samples from breast cancer patients and tissue samples from BBD controls. On the other hand, somatic MnlI site mutations, defined as a difference in MnlI RFLP pattern between tumor tissue and the corresponding, adjacent, non-tumor tissue, occurred more frequently in breast cancer patients (28.3%) than in BBD patients (15.3%) (P = 0.05) and more frequently in proliferative BBD (13.0%) than in non-proliferative BBD (7.1%). Our data suggest that somatic MnlI site mutations may play a role in the pathogenesis of breast cancer.