No increased risk of relapse of breast cancer for women who give birth after assisted conception

Prognostic effect of subsequent childbirth after the diagnosis of breast cancer using propensity score matching analysis

BACKGROUND

Among younger patients, one of the important concerns is whether they can give birth safely. Although previous studies have investigated this topic, many aspects remain unclear owing to potential biases. We aimed to evaluate the prognostic effect of subsequent childbirth after the diagnosis using propensity score matching.

METHODS

A single-center retrospective cohort study was conducted. This study included patients aged ≤ 45 years, diagnosed with breast cancer between 2005 and 2014. Patients with and without subsequent childbirth were assigned to the childbirth and non-childbirth cohorts, respectively. Relapse-free survival (RFS) and overall survival (OS) of the childbirth cohort were compared with those of the non-childbirth cohort. The covariates in the propensity score model included age, tumor size, node status, number of preceding childbirths before the diagnosis, estrogen receptor, and human epidermal growth factor receptor 2 status.

RESULTS

104 patients with childbirth and 2250 without childbirth were assigned to the respective cohorts. At a median follow-up of 82 months, the childbirth cohort showed a significantly longer RFS than the non-childbirth cohort (HR = 0.469 [0.221-0.992]; p = 0.047). There was no significant difference in the OS (HR = 0.208 [0.029-1.494]; p = 0.119). After matching, subsequent childbirth was not significantly associated with RFS (HR = 0.436 [0.163-1.164], p = 0.098) and OS (HR = 0.372 [0.033-4.134], p = 0.402).

CONCLUSIONS

Subsequent childbirth was not associated with an increased risk of relapse and mortality. It is important to make younger patients aware of these novel findings and aid them in their decision-making.

The Impact of Malignancy on Assisted Reproductive Outcomes for Cancer Survivors: A Retrospective Case–Control Study

Background

Related studies have shown that it is safe for cancer patients to undergo assisted reproduction. However, studies on whether a history of cancer affects long-term reproductive outcomes in women who undergo assisted reproductive technology (ART) are scarce. In this study, we evaluated the long-term reproductive outcomes of patients with malignant tumors undergoing ART treatment and explored the impact of malignancy history on ART outcomes.

Methods

This retrospective study analyzed the clinical outcomes of patients with malignant tumors undergoing their first in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles compared with those of age-matched healthy infertile women at Fujian Maternity and Child Health Hospital between January 2003 and October 2020. We evaluated ovarian stimulation outcome, the pregnancy rate, the live birth rate, the risk of adverse obstetric outcomes and birth outcomes.

Results

This study included 59 patients in the cancer group for data analysis who had a history of malignancy. By matching, a total of 118 healthy infertile women were included in the control group. No statistically significant association was found in terms of age, duration of infertility, BMI, or insemination type between the two groups of patients. Thyroid cancer(45.8%) and gynecologic malignancies (44.07%) were the major cancer types in this study. There were statistically significant differences in the antral follicle count (AFC) (12.00 ± 7.86 vs. 14.90 ± 8.71, P=0.033), length of ovarian stimulation (9.98 ± 2.68 vs. 11.42 ± 2.43, P=0.033) and endometrial thickness on the trigger day (10.16 ± 3.11 vs. 10.84 ± 2.17, P<0.001) between the two groups. The total gonadotropin dose, number of oocytes retrieved, fertilization rate, cleavage rate, high-quality embryo rate, blastocyst rate and first-time embryo-transfer (ET) implantation rate were nonsignificantly lower in the cancer group than in the control group (P>0.05). There were no significant differences in the clinical pregnancy rate per ET cycle (32% vs. 40.39%, P=0.156), live birth rate per ET cycle (27% vs. 35.96%, P=0.119), miscarriage rate per ET cycle (5% vs. 4.43%, P=0.779), or preterm delivery rate per ET cycle (11.11% vs. 17.80%, P=0.547) between the two groups. Additionally, regression analysis showed that a history of malignancy was not a risk factor for reproductive outcomes.

Conclusions

Overall, it is feasible for women with a history of cancer to conceive using ART is feasible and their long-term reproductive outcomes are similar to these of healthy infertile women. A history of cancer does not decrease the number of retrieved oocytes, increase the risk of adverse obstetric outcomes or affect birth outcomes.

Survival outcomes following pregnancy or assisted reproductive technologies after breast cancer: A population-based study

BACKGROUND

This study sought to determine the impact of pregnancy or assisted reproductive technologies (ART) on breast-cancer-specific survival among breast cancer survivors.

METHODS

The authors performed a cohort study using a novel data linkage from the California Cancer Registry, the California birth cohort, and the Society for Assisted Reproductive Technology Clinic Outcome Reporting System data sets. They performed risk-set matching in women with stages I-III breast cancer diagnosed between 2000 and 2012. For each pregnant woman, comparable women who were not pregnant at that point but were otherwise similar based on observed characteristics were matched at the time of pregnancy. After matching, Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of pregnancy with breast-cancer-specific survival. We repeated these analyses for women who received ART.

RESULTS

Among 30,021 women with breast cancer, 553 had a pregnancy and 189 attempted at least one cycle of ART. In Cox proportional hazards modeling, the pregnancy group had a higher 5-year disease-specific survival rate; 95.6% in the pregnancy group and 90.6% in the nonpregnant group (HR, 0.43; 95% CI, 0.24-0.77). In women with hormone receptor-positive cancer, we found similar results (HR, 0.43; 95% CI, 0.2-0.91). In the ART analysis, there was no difference in survival between groups; the 5-year disease-specific survival rate was 96.9% in the ART group and 94.1% in the non-ART group (HR, 0.44; 95% CI, 0.17-1.13).

CONCLUSION

Pregnancy and ART are not associated with worse survival in women with breast cancer.

LAY SUMMARY

We sought to determine the impact of pregnancy or assisted reproductive technologies (ART) among breast cancer survivors. We performed a study of 30,021 women by linking available data from California and the Society for Assisted Reproductive Technology Clinic Outcome Reporting System. For each pregnant woman, we matched at the time of pregnancy comparable women who were not pregnant at that point but were otherwise similar based on observed characteristics. We repeated these analyses for women who received ART. We found that pregnancy and ART were not associated with worse survival.

Fertility preservation for women with breast cancer: a multicentre randomized controlled trial on various ovarian stimulation protocols

STUDY QUESTION

Does ovarian stimulation with the addition of tamoxifen or letrozole affect the number of cumulus-oocyte complexes (COCs) retrieved compared to standard ovarian stimulation in women with breast cancer who undergo fertility preservation?

SUMMARY ANSWER

Alternative ovarian stimulation protocols with tamoxifen or letrozole did not affect the number of COCs retrieved at follicle aspiration in women with breast cancer.

WHAT IS KNOWN ALREADY

Alternative ovarian stimulation protocols have been introduced for women with breast cancer who opt for fertility preservation by means of banking of oocytes or embryos. How these ovarian stimulation protocols compare to standard ovarian stimulation in terms of COC yield is unknown.

STUDY DESIGN, SIZE, DURATION

This multicentre, open-label randomized controlled superiority trial was carried out in 10 hospitals in the Netherlands and 1 hospital in Belgium between January 2014 and December 2018. We randomly assigned women with breast cancer, aged 18–43 years, who opted for banking of oocytes or embryos to one of three study arms; ovarian stimulation plus tamoxifen, ovarian stimulation plus letrozole or standard ovarian stimulation. Standard ovarian stimulation included GnRH antagonist, recombinant FSH and GnRH agonist trigger. Randomization was performed with a web-based system in a 1:1:1 ratio, stratified for oral contraception usage at start of ovarian stimulation, positive estrogen receptor (ER) status and positive lymph nodes. Patients and caregivers were not blinded to the assigned treatment. The primary outcome was number of COCs retrieved at follicle aspiration.

PARTICIPANTS/MATERIALS, SETTING, METHODS

During the study period, 162 women were randomly assigned to one of three interventions. Fifty-four underwent ovarian stimulation plus tamoxifen, 53 ovarian stimulation plus letrozole and 55 standard ovarian stimulation. Analysis was according to intention-to-treat principle.

MAIN RESULTS AND THE ROLE OF CHANCE

No differences among groups were observed in the mean (±SD) number of COCs retrieved: 12.5 (10.4) after ovarian stimulation plus tamoxifen, 14.2 (9.4) after ovarian stimulation plus letrozole and 13.6 (11.6) after standard ovarian stimulation (mean difference −1.13, 95% CI −5.70 to 3.43 for tamoxifen versus standard ovarian stimulation and 0.58, 95% CI −4.03 to 5.20 for letrozole versus standard ovarian stimulation). After adjusting for oral contraception usage at the start of ovarian stimulation, positive ER status and positive lymph nodes, the mean difference was −1.11 (95% CI −5.58 to 3.35) after ovarian stimulation plus tamoxifen versus standard ovarian stimulation and 0.30 (95% CI −4.19 to 4.78) after ovarian stimulation plus letrozole versus standard ovarian stimulation. There were also no differences in the number of oocytes or embryos banked. There was one serious adverse event after standard ovarian stimulation: one woman was admitted to the hospital because of ovarian hyperstimulation syndrome.

LIMITATIONS, REASONS FOR CAUTION

The available literature on which we based our hypothesis, power analysis and sample size calculation was scarce and studies were of low quality. Our study did not have sufficient power to perform subgroup analysis on follicular, luteal or random start of ovarian stimulation.

WIDER IMPLICATIONS OF THE FINDINGS

Our study showed that adding tamoxifen or letrozole to a standard ovarian stimulation protocol in women with breast cancer does not impact the effectiveness of fertility preservation and paves the way for high-quality long-term follow-up on breast cancer treatment outcomes and women’s future pregnancy outcomes. Our study also highlights the need for high-quality studies for all women opting for fertility preservation, as alternative ovarian stimulation protocols have been introduced to clinical practice without proper evidence.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by a grant (2011.WO23.C129) of ‘Stichting Pink Ribbon’, a breast cancer fundraising charity organization in the Netherlands. M.G., C.B.L. and R.S. declared that the Center for Reproductive Medicine, Amsterdam UMC (location VUMC) has received unconditional research and educational grants from Guerbet, Merck and Ferring, not related to the presented work. C.B.L. declared a speakers fee for Inmed and Yingming. S.C.L. reports grants and non-financial support from Agendia, grants, non-financial support and other from AstraZeneca, grants from Eurocept-pharmaceuticals, grants and non-financial support from Genentech/Roche and Novartis, grants from Pfizer, grants and non-financial support from Tesaro and Immunomedics, other from Cergentis, IBM, Bayer, and Daiichi-Sankyo, outside the submitted work; In addition, S.C.L. has a patent UN23A01/P-EP pending that is unrelated to the present work. J.M.J.S. reported payments and travel grants from Merck and Ferring. C.C.M.B. reports her role as unpaid president of the National guideline committee on Fertility Preservation in women with cancer. K.F. received unrestricted grants from Merck Serono, Good Life and Ferring not related to present work. K.F. declared paid lectures for Ferring. D.S. declared former employment from Merck Sharp & Dohme (MSD). K.F. declared paid lectures for Ferring. D.S. reports grants from MSD, Gedeon Richter and Ferring paid to his institution; consulting fee payments from MSD and Merck Serono paid to his institution; speaker honoraria from MSD, Gedeon Richter, Ferring Pharmaceuticals and Merck Serono paid to his institution. D.S. has also received travel and meeting support from MSD, Gedeon Richter, Ferring Pharmaceuticals and Merck Serono. No payments are related to present work.

TRIAL REGISTRATION NUMBER

NTR4108.

TRIAL REGISTRATION DATE

6 August 2013.

DATE OF FIRST PATIENT’S ENROLMENT

30 January 2014.

Safety of fertility preservation techniques before and after anticancer treatments in young women with breast cancer: a systematic review and meta-analysis

STUDY QUESTION

Is it safe to perform controlled ovarian stimulation (COS) for fertility preservation before starting anticancer therapies or ART after treatments in young breast cancer patients?

SUMMARY ANSWER

Performing COS before, or ART following anticancer treatment in young women with breast cancer does not seem to be associated with detrimental prognostic effect in terms of breast cancer recurrence, mortality or event-free survival (EFS).

WHAT IS KNOWN ALREADY

COS for oocyte/embryo cryopreservation before starting chemotherapy is standard of care for young women with breast cancer wishing to preserve fertility. However, some oncologists remain concerned on the safety of COS, particularly in patients with hormone-sensitive tumors, even when associated with aromatase inhibitors. Moreover, limited evidence exists on the safety of ART in breast cancer survivors for achieving pregnancy after the completion of anticancer treatments.

STUDY DESIGN, SIZE, DURATION

The present systematic review and meta-analysis was carried out by three blinded investigators using the keywords 'breast cancer' and 'fertility preservation'; keywords were combined with Boolean operators. Eligible studies were identified by a systematic literature search of Medline, Web of Science, Embase and Cochrane library with no language or date restriction up to 30 June 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

To be included in this meta-analysis, eligible studies had to be case-control or cohort studies comparing survival outcomes of women who underwent COS or ART before or after breast cancer treatments compared to breast cancer patients not exposed to these strategies. Survival outcomes of interest were cancer recurrence rate, relapse rate, overall survival and number of deaths. Adjusted relative risk (RR) and hazard ratio (HR) with 95% CI were extracted. When the number of events for each group were available but the above measures were not reported, HRs were estimated using the Watkins and Bennett method. We excluded case reports or case series with <10 patients and studies without a control group of breast cancer patients who did not pursue COS or ART. Quality of data and risk of bias were assessed using the Newcastle-Ottawa Assessment Scale.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1835 records were retrieved. After excluding ineligible publications, 15 studies were finally included in the present meta-analysis (n = 4643). Among them, 11 reported the outcomes of breast cancer patients who underwent COS for fertility preservation before starting chemotherapy, and 4 the safety of ART following anticancer treatment completion. Compared to women who did not receive fertility preservation at diagnosis (n = 2386), those who underwent COS (n = 1594) had reduced risk of recurrence (RR 0.58, 95% CI 0.46-0.73) and mortality (RR 0.54, 95% CI 0.38-0.76). No detrimental effect of COS on EFS was observed (HR 0.76, 95% CI 0.55-1.06). A similar trend of better outcomes in terms of EFS was observed in women with hormone-receptor-positive disease who underwent COS (HR 0.36, 95% CI 0.20-0.65). A reduced risk of recurrence was also observed in patients undergoing COS before neoadjuvant chemotherapy (RR 0.22, 95% CI 0.06-0.80). Compared to women not exposed to ART following completion of anticancer treatments (n = 540), those exposed to ART (n = 123) showed a tendency for better outcomes in terms of recurrence ratio (RR 0.34, 95% CI 0.17-0.70) and EFS (HR 0.43, 95% CI 0.17-1.11).

LIMITATIONS, REASONS FOR CAUTION

This meta-analysis is based on abstracted data and most of the studies included are retrospective cohort studies. Not all studies had matching criteria between the study population and the controls, and these criteria often differed between the studies. Moreover, rate of recurrence is reported as a punctual event and it is not possible to establish when recurrences occurred and whether follow-up, which was shorter than 5 years in some of the included studies, is adequate to capture late recurrences.

WIDER IMPLICATIONS OF THE FINDINGS

Our results demonstrate that performing COS at diagnosis or ART following treatment completion does not seem to be associated with detrimental prognostic effect in young women with breast cancer, including among patients with hormone receptor-positive disease and those receiving neoadjuvant chemotherapy.

STUDY FUNDING/COMPETING INTEREST(S)

Partially supported by the Associazione Italiana per la Ricerca sul Cancro (AIRC; grant number MFAG 2020 ID 24698) and the Italian Ministry of Health-5 × 1000 funds 2017 (no grant number). M.L. acted as consultant for Roche, Pfizer, Novartis, Lilly, AstraZeneca, MSD, Exact Sciences, Gilead, Seagen and received speaker honoraria from Roche, Pfizer, Novartis, Lilly, Ipsen, Takeda, Libbs, Knight, Sandoz outside the submitted work. F.S. acted as consultant for Novartis, MSD, Sun Pharma, Philogen and Pierre Fabre and received speaker honoraria from Roche, Novartis, BMS, MSD, Merck, Sun Pharma, Sanofi and Pierre Fabre outside the submitted work. I.D. has acted as a consultant for Roche, has received research grants from Roche and Ferring, has received reagents for academic clinical trial from Roche diagnostics, speaker's fees from Novartis, and support for congresses from Theramex and Ferring outside the submitted work. L.D.M. reported honoraria from Roche, Novartis, Eli Lilly, MSD, Pfizer, Ipsen, Novartis and had an advisory role for Roche, Eli Lilly, Novartis, MSD, Genomic Health, Pierre Fabre, Daiichi Sankyo, Seagen, AstraZeneca, Eisai outside the submitted work. The other authors declare no conflict of interest. The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript and decision to submit the manuscript for publication.

REGISTRATION NUMBER

N/A.

Safety of assisted reproductive techniques in young women harboring germline pathogenic variants in BRCA1/2 with a pregnancy after prior history of breast cancer

BACKGROUND

Knowledge is growing on the safety of assisted reproductive techniques (ART) in cancer survivors. No data exist, however, for the specific population of breast cancer patients harboring germline BRCA1/2 pathogenic variants.

PATIENTS AND METHODS

This is a multicenter retrospective cohort study across 30 centers worldwide including women diagnosed at ≤40 years with stage I-III breast cancer, between January 2000 and December 2012, harboring known germline BRCA1/2 pathogenic variants. Patients included in this analysis had a post-treatment pregnancy either achieved through use of ART (ART group) or naturally (non-ART group). ART procedures included ovulation induction, ovarian stimulation for in vitro fertilization or intracytoplasmic sperm injection, and embryo transfer under hormonal replacement therapy.

RESULTS

Among the 1424 patients registered in the study, 168 were eligible for inclusion in the present analysis, of whom 22 were in the ART group and 146 in the non-ART group. Survivors in the ART group conceived at an older age compared with those in the non-ART group (median age: 39.7 versus 35.4 years, respectively). Women in the ART group experienced more delivery complications compared with those in the non-ART group (22.1% versus 4.1%, respectively). No other apparent differences in obstetrical outcomes were observed between cohorts. The median follow-up from pregnancy was 3.4 years (range: 0.8-8.6 years) in the ART group and 5.0 years (range: 0.8-17.6 years) in the non-ART group. Two patients (9.1%) in the ART group experienced a disease-free survival event (specifically, a locoregional recurrence) compared with 40 patients (27.4%) in the non-ART group. In the ART group, no patients deceased compared with 10 patients (6.9%) in the non-ART group.

CONCLUSION

This study provides encouraging safety data on the use of ART in breast cancer survivors harboring germline pathogenic variants in BRCA1/2, when natural conception fails or when they opt for ART in order to carry out preimplantation genetic testing.

Dynamic changes in serum steroid hormone during the first trimester of pregnancy between infertile women conceiving with and without hormone replacement therapy

Objective

Recent advances in cancer treatment and reproductive medicine have made the post-treatment quality of life an important concern for cancer survivors. We aimed to evaluate the safety of sex hormone (estradiol and progesterone) replacement therapy (HRT) in women who conceived by assisted reproductive technology (ART) with hormone receptor-positive breast cancer.

Methods

We measured serum E2 and P4 levels at 4–10 weeks of gestation in women who conceived naturally or after timed intercourse or intrauterine insemination for infertility without HRT for luteal support (non-HR group; n = 135). We conducted a retrospective comparison of the values from the non-HR group with those of women who conceived by ART with HRT for infertility (HR group; n = 75).

Results

Serum E2 levels were significantly higher in the non-HR group than in the HR group at 5, 6, and 8 weeks of gestation. Similarly, serum P4 levels were significantly higher in the non-HR group than in the HR group at 4, 5, and 6 weeks of gestation.

Conclusions

This study suggests that in cancer reproductive medicine for hormone-dependent breast cancer survivors, HRT administered during the first trimester of a pregnancy after primary disease treatment may not increase the sex hormone levels to levels above those seen in spontaneous pregnancy.

Success and risks of pregnancy after breast cancer

INTRODUCTION

Breast cancer is the most common cancer in women worldwide. The number of childbearing-age women diagnosed with early breast cancer (eBC) is increasing, raising questions over their subsequent fertility.

PURPOSE

The main objective of this study was therefore to assess, in a cohort of eBC patients with pregnancy desire, the rate of live births achieved spontaneously or by assisted reproductive technology.

METHODS

We conducted an observational, descriptive, retrospective study including patients aged 18-40, treated for eBC at the Institut de Cancérologie de l'Ouest (ICO) Pays de Loire between July 2010 and July 2016, with pregnancy desire. The primary outcome was the rate of live births. Secondary outcomes were overall survival, disease-free survival, time to conception, and spontaneous or assisted pregnancy rate.

RESULTS

61 patients were included, with a live birth rate of 19.7% (12/61). We observed no recurrence or death in women with a pregnancy. Pregnancy started with a median time of 36.4 months after the end of treatment (4.1-51.3 months). All pregnancies in this cohort were achieved spontaneously.

CONCLUSION

The results of our cohort are consistent with previous results showing that spontaneous pregnancy remains possible after treatment for eBC without increasing the risk of recurrence or death.

Gonadotrophin stimulation and risk of relapse in breast cancer

STUDY QUESTION

Is gonadotrophin stimulation as part of IVF associated with an increased risk of relapse in breast cancer?

SUMMARY ANSWER

Controlled ovarian stimulation (COS) in connection with IVF in women with previous breast cancer was not associated with an increased risk of breast cancer relapse.

WHAT IS KNOWN ALREADY

Breast cancer is the most common malignancy among women worldwide and the leading cause of cancer death among females. The use of COS with gonadotrophins with subsequent cryopreservation of oocytes or embryos in order to enhance the chances of pregnancy after cancer treatment is the current most established fertility preservation method for women with breast cancer. To date, there are only a few small retrospective hospital-based controlled studies evaluating the risk of breast cancer relapse in patients undergoing fertility preservation with or without COS, showing no evident risk of relapse in breast cancer after the use of gonadotoxic agents.

STUDY DESIGN, SIZE, DURATION

This was a retrospective, population-based cohort study comprising 5857 women with previous breast cancer of whom 337 were exposed to COS. Exposure (COS) and outcomes (relapse and death) were identified for all patients from 2005 to 2014 by assessing the National Quality Register for Assisted Reproduction, the Swedish Medical Birth Register, the National Patient Register, the Swedish Prescribed Drug Register, the Swedish Cause of Death Register, the National Breast Cancer Register and the Swedish Cancer Register. Matching according to set criteria was possible for 334 women, who constituted the control group. A total of 274 women had undergone IVF after completing breast cancer treatment and 63 women had undergone COS for fertility preservation at the time of breast cancer diagnosis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women aged 20–44 years previously diagnosed with breast cancer and exposed to COS were matched for age at breast cancer diagnosis ±5 years, tumour size and lymph node involvement with a non-exposed control group, including women with known T- and N-stages. In a subsequent analysis, the matched cohort was assessed by also including women with unknown T- and N-stages. A secondary analysis comprised the entire non-matched cohort, including all women with known T- and N-stages. Also here, a subsequent analysis included women with missing data for T- and N-stages. The risk of relapse in breast cancer was estimated as crude hazard ratios (HRs) and 95% CI using Cox proportional hazards models in the primary and secondary analyses where T- and N-stages were known: otherwise the risks of relapse were only given descriptively.

MAIN RESULTS AND THE ROLE OF CHANCE

In the primary matched analysis, relapse occurred in 20 of 126 women exposed to COS (15.9%) compared with 39 of 126 (31.0%) in the control cohort (HR = 0.70; 95% CI 0.39–1.45; P = 0.22). In the subsequent analysis, also including women with unknown T- and N-stages, relapse occurred in 27 of 337 (8.0%) women having undergone COS compared with 71/334 (21.3%) among the non-exposed. In the secondary adjusted analysis, relapse occurred in 20 of 126 (15.9%) exposed women and in 918 of 3729 (24.6%) non-exposed women (HR = 0.81; 95% CI 0.49–1.33; P = 0.70). In the subsequent analysis, including unknown T- and N-stages, relapse occurred in 27 of 337 (8.0%) women in the exposed group and 1176 of 5520 (21.3%) in the non-exposed cohort.

LIMITATIONS, REASONS FOR CAUTION

A substantial degree of missing data on important prognostic variables was a limitation, particularly when analysing the total cohort. Furthermore, data on confounding factors, such as BMI, were not completely covered. Another limitation was that a pre-specified variable for relapse was not in use for the majority of the National Breast Cancer Register. Furthermore, the follow-up time from available register data (2005–2014) is rather short. Finally, we cannot be sure whether the prognostic information from receptor status, showing a lower incidence in the exposed group, is representative. Information on T- and N-stages was missing in more than half of the patients.

WIDER IMPLICATIONS OF THE FINDINGS

In this large, retrospective, matched cohort study, we found no increased risk of relapse in breast cancer among women who had been exposed to gonadotrophins as part of IVF. This is reassuring but might be confounded by the selection of a group of women with a more favourable prognosis than those not undergoing IVF. The present study strengthens previous findings by being large, national and register based. Its results are applicable to women undergoing fertility preservation as well as to those undergoing regular IVF treatment.

STUDY FUNDING/COMPETING INTEREST(S)

Supported in part by grants from the Swedish state under the agreement between the Swedish government and the county councils the ALF-agreement (ALFGBG-720291), The Assar Gabrielsson Fund (FB 15-20), The Breast Cancer Fund and the Swedish Association of Local authorities and Regions, SKR. There are no conflicts of interest to declare.

TRIAL REGISTRATION

N/A