Pregnancy After Breast Cancer in Young BRCA Carriers: An International Hospital-Based Cohort Study.

Importance: Young women with breast cancer who have germline pathogenic variants in BRCA1 or BRCA2 face unique challenges regarding fertility. Previous studies demonstrating the feasibility and safety of pregnancy in breast cancer survivors included limited data regarding BRCA carriers. Objective: To investigate cumulative incidence of pregnancy and disease-free survival in young women who are BRCA carriers. Design, Setting, and Participants: International, multicenter, hospital-based, retrospective cohort study conducted at 78 participating centers worldwide. The study included female participants diagnosed with invasive breast cancer at age 40 years or younger between January 2000 and December 2020 carrying germline pathogenic variants in BRCA1 and/or BRCA2. Last delivery was October 7, 2022; last follow-up was February 20, 2023. Exposure: Pregnancy after breast cancer. Main Outcomes and Measures: Primary end points were cumulative incidence of pregnancy after breast cancer and disease-free survival. Secondary end points were breast cancer-specific survival, overall survival, pregnancy, and fetal and obstetric outcomes. Results: Of 4732 BRCA carriers included, 659 had at least 1 pregnancy after breast cancer and 4073 did not. Median age at diagnosis in the overall cohort was 35 years (IQR, 31-38 years). Cumulative incidence of pregnancy at 10 years was 22% (95% CI, 21%-24%), with a median time from breast cancer diagnosis to conception of 3.5 years (IQR, 2.2-5.3 years). Among the 659 patients who had a pregnancy, 45 (6.9%) and 63 (9.7%) had an induced abortion or a miscarriage, respectively. Of the 517 patients (79.7%) with a completed pregnancy, 406 (91.0%) delivered at term (≥37 weeks) and 54 (10.4%) had twins. Among the 470 infants born with known information on pregnancy complications, 4 (0.9%) had documented congenital anomalies. Median follow-up was 7.8 years (IQR, 4.5-12.6 years). No significant difference in disease-free survival was observed between patients with or without a pregnancy after breast cancer (adjusted hazard ratio, 0.99; 95% CI, 0.81-1.20). Patients who had a pregnancy had significantly better breast cancer-specific survival and overall survival. Conclusions and Relevance: In this global study, 1 in 5 young BRCA carriers conceived within 10 years after breast cancer diagnosis. Pregnancy following breast cancer in BRCA carriers was not associated with decreased disease-free survival. Trial Registration: ClinicalTrials.gov Identifier: NCT03673306.

Immune microenvironment dynamics in breast cancer during pregnancy: impact of gestational age on tumor-infiltrating lymphocytes and prognosis.

Background: Breast cancer during pregnancy (PrBC) is a rare condition known for its aggressive clinical behavior. The presence of tumor-infiltrating lymphocytes (TILs) has been shown to have a significant impact on the prognosis of these patients. Despite some biological characteristics of the tumor that may differ depending on the gestational age, little is known about the dynamics of the immune landscape within the tumor microenvironment (TME) in PrBC. Therefore, in this study, our objective was to gain comprehensive insights into the relationship between gestational age at breast cancer diagnosis and the composition of the TME. Methods: n = 108 PrBC were selected from our institutional registry and categorized based on the gestational age by trimester. For all cases, TILs were profiled according to the International TILs Working Group recommendations, and subtyped by CD4, CD8, and forkhead box P3 (FOXP3) immunohistochemistry. PD-L1 was tested according to the combined positive score (CPS) using the IHC 22C3 pharmDx assay, with a cutoff value of ≥10 for positivity. The statistical approach encompassed Fisher's and Chi-squared tests, with appropriate adjustments for multiple comparisons, logistic regression models, and survival analyses based on the Kaplan-Meier method. Results: The proportion of patients with poorly differentiated (G3) neoplasms increased as the gestational age advanced (first trimester, n = 25, 56.8%; second trimester, n = 27, 69.2%; third trimester, n = 21, 87.5%; p = 0.03). The histologic subtypes as well as the hormone receptor (HR) and HER2 status did not show significant changes across different pregnancy trimesters. In the HR+/HER2- subtype, there was a higher proportion of tumors with high/moderate TILs in the early phases of pregnancy, similar to FOXP3 expression (TILs: first trimester, n = 10, 35.7%; second trimester, n = 2, 10.5%; third trimester, n = 0; p = 0.02; FOXP3: first trimester, n = 10, 40%; second trimester, n = 3, 15.8%; third trimester, n = 0; p = 0.03). The median follow-up for our cohort was 81 months. Patients who relapsed after a breast cancer diagnosis during the first trimester were more frequently PD-L1-negative, unlike those with no disease recurrence (n = 9, 100% vs. n = 9, 56.3%; p = 0.03; hormone therapy and n = 9, 100% vs. n = 7, 53.9%; p = 0.02; chemotherapy). No statistically significant differences were seen among the three trimesters in terms of survival outcome. Conclusion: The TME dynamics of HR+/HER2- PrBC vary based on gestational age, suggesting that immune tolerance expression during later gestational age could explain the increased aggressiveness of tumors diagnosed at that stage.

From Pregnancy to Lactation: When the Pathway is Complicated by Cancer.

BACKGROUND: Women with a cancer history report high distress during pregnancy and infant feeding. Despite the clear advantages of breastfeeding, little is known about factors influencing infant feeding behavior in women with cancer history. RESEARCH AIM: This three-time point longitudinal study aimed to explore the centrality of pregnancy and infant feeding experiences in 17 pregnant women with a cancer history (cases) compared to 17 pregnant women without cancer history (controls). METHODS: During pregnancy, participants filled out the Centrality of Events Scale and an ad hoc questionnaire about specific emotions, concerns, and expectations about infant feeding (T1), and their childbirth and infant feeding experiences during hospitalization (T2), and at 3-months postpartum (T3). RESULTS: Results at T1 demonstrated that participants with a history of cancer reported a higher perception of negative judgment and moral choice about breastfeeding than participants without a history of cancer. At T2 they reported a more positive childbirth experience than controls. From T2 to T3 participants with a history of cancer breastfed at a higher percentage than controls, and at T3 they reported higher levels of emotional and physical pleasure about the infant feeding experiences. CONCLUSIONS: Women with cancer history may experience a higher emotional and physical pleasure with infant feeding. Despite initial difficulties, a greater prevalence of breastfeeding was present for women with a history of cancer. Although this is a small sample, this research suggests that support and promotion of breastfeeding might be very effective after a serious medical diagnosis.

Interrupting Endocrine Therapy to Attempt Pregnancy after Breast Cancer.

BACKGROUND: Prospective data on the risk of recurrence among women with hormone receptor-positive early breast cancer who temporarily discontinue endocrine therapy to attempt pregnancy are lacking. METHODS: We conducted a single-group trial in which we evaluated the temporary interruption of adjuvant endocrine therapy to attempt pregnancy in young women with previous breast cancer. Eligible women were 42 years of age or younger; had had stage I, II, or III disease; had received adjuvant endocrine therapy for 18 to 30 months; and desired pregnancy. The primary end point was the number of breast cancer events (defined as local, regional, or distant recurrence of invasive breast cancer or new contralateral invasive breast cancer) during follow-up. The primary analysis was planned to be performed after 1600 patient-years of follow-up. The prespecified safety threshold was the occurrence of 46 breast cancer events during this period. Breast cancer outcomes in this treatment-interruption group were compared with those in an external control cohort consisting of women who would have met the entry criteria for the current trial. RESULTS: Among 516 women, the median age was 37 years, the median time from breast cancer diagnosis to enrollment was 29 months, and 93.4% had stage I or II disease. Among 497 women who were followed for pregnancy status, 368 (74.0%) had at least one pregnancy and 317 (63.8%) had at least one live birth. In total, 365 babies were born. At 1638 patient-years of follow-up (median follow-up, 41 months), 44 patients had a breast cancer event, a result that did not exceed the safety threshold. The 3-year incidence of breast cancer events was 8.9% (95% confidence interval [CI], 6.3 to 11.6) in the treatment-interruption group and 9.2% (95% CI, 7.6 to 10.8) in the control cohort. CONCLUSIONS: Among select women with previous hormone receptor-positive early breast cancer, temporary interruption of endocrine therapy to attempt pregnancy did not confer a greater short-term risk of breast cancer events, including distant recurrence, than that in the external control cohort. Further follow-up is critical to inform longer-term safety. (Funded by ETOP IBCSG Partners Foundation and others; POSITIVE ClinicalTrials.gov number, NCT02308085.).

Immune plasticity in pregnancy-associated breast cancer tumorigenesis.

Pregnancy-associated breast cancer (PrBC) is a rare tumor that requires complex management. The coexistence of cancer and pregnancy involves several proliferative, invasive, and immune tolerance mechanisms that are shared between the two conditions. In normal pregnancy, successful fetal development is achieved through suppression of the maternal immune response toward the fetus. Similar immunosuppressive patterns during the malignant transformation supporting tumor growth, progression, and metastasis are also exhibited by tumors. An improved understanding of the immunosuppressive mechanisms and pathways underlying the immunological synergy in PrBC could lead to the identification of novel biomarkers that potentially improve patients' clinical management. In this review article, we outline some of the paramount features of immune plasticity during pregnancy, discussing the similarities shared between normal pregnancy and breast cancer in terms of immune suppression mechanisms. Emphasis is also placed on how the current knowledge of the immune milieu of these conditions may be translated into consequent therapeutic opportunities.

Impact of Anti-HER2 Therapy Alone and With Weekly Paclitaxel on the Ovarian Reserve of Young Women With HER2-Positive Breast Cancer.

BACKGROUND: The potential gonadotoxicity of anti-HER2 agents remains largely unknown, and limited, conflicting evidence exists for taxanes. Antimüllerian hormone (AMH) is an established biomarker of ovarian reserve that may aid in quantifying anticancer treatment-induced gonadotoxicity. PATIENTS AND METHODS: The present biomarker analysis of the randomized phase III neoadjuvant NeoALTTO trial included premenopausal women aged ≤45 years at diagnosis of HER2-positive early breast cancer with available frozen serum samples at baseline (ie, before anticancer treatments), at week 2 (ie, the "biological window" of anti-HER2 therapy alone), and/or at the time of surgery (ie, after completing paclitaxel + anti-HER2 therapy, before starting adjuvant chemotherapy). RESULTS: The present analysis included 130 patients with a median age of 38 years (interquartile ratio [IQR], age 33-42 years). AMH values at the 3 time points differed significantly (P<.001). At baseline, median AMH levels were 1.29 ng/mL (IQR, 0.56-2.62 ng/mL). At week 2, a small but significant reduction in AMH levels was observed (median, 1.10 ng/mL; IQR, 0.45-2.09 ng/mL; P<.001). At surgery, a larger significant decline in AMH levels was observed (median, 0.01 ng/mL; IQR, 0.01-0.03 ng/mL; P<.001). Although the type of anti-HER2 treatment (trastuzumab and/or lapatinib) did not seem to impact the results, age and pretreatment ovarian reserve had a major influence on treatment-induced gonadotoxicity risk. CONCLUSIONS: This NeoALTTO biomarker analysis showed that anti-HER2 therapies alone had limited gonadotoxicity but that the addition of weekly paclitaxel resulted in marked AMH decline with possible negative implications for subsequent ovarian function and fertility.

Contraception and Hormone Replacement Therapy in Healthy Carriers of Germline BRCA1/2 Genes Pathogenic Variants: Results from an Italian Survey.

Several myths and misconceptions exist about hormones in women with familial predisposition to cancer, and there are few real-life data on their prescription and uptake. To better understand how they are prescribed and accepted in healthy carriers of a BRCA1/2 pathogenetic variant, an online survey was uploaded on Google Forms and shared through social media closed groups of patients' associations, aBRCAcadabra and ACTO Campania. A total of 241 questionnaires were collected. Sexual quality of life was considered of the utmost importance by most of the respondents (mean score of 7 ± 2.8/10), but they felt the counseling they received by healthcare professionals on the topic was insufficient (4.9 ± 3.2/10). Only 57 women out of 233 (24.5%) had used hormonal contraception after being diagnosed as carriers of a BRCA pathogenetic variant, and 42 out of 148 (28.4%) underwent menopause hormonal therapy. The majority of women (53.6% for contraception and 61.5% for menopause) reported being dissatisfied with the counseling received, and 58.2% were not aware of the protective effect of hormonal contraception on the risk of ovarian cancer. An educational effort is desirable to guarantee healthy BRCA carriers reliable contraception and evidence-based menopause counseling.

Breast Cancer during Pregnancy as a Special Type of Early-Onset Breast Cancer: Analysis of the Tumor Immune Microenvironment and Risk Profiles.

Breast cancer during pregnancy (PrBC) is a rare tumor with only a little information on its immune landscape. Here, we sought to characterize the cellular composition of the tumor microenvironment (TME) of PrBC and identify its differences from early-onset breast cancer (EOBC) in non-pregnant women. A total of 83 PrBC and 89 EOBC were selected from our Institutional registry and subjected to tumor-infiltrating lymphocytes (TILs) profiling and immunohistochemistry for CD4, CD8, forkhead box P3 (FOXP3), and programmed death-ligand 1 (PD-L1) (clone 22C3). A significantly lower frequency of hormone receptor (HR)-positive tumors was observed in PrBC. The prevalence of low/null PD-L1 and CD8+TILs was higher in PrBC than in the controls, specifically in HR+/HER2- breast cancers. PrBC had a significantly higher risk of relapse and disease-related death, compared to EOBC. The presence of TILs and each TIL subpopulation were significantly associated with disease relapse. Moreover, the death rate was higher in PrBC with CD8+ TILs. The TME of PrBC is characterized by specific patterns of TIL subpopulations with significant biological and prognostic roles. Routine assessment of TILs and TILs subtyping in these patients would be a valid addition to the pathology report that might help identify clinically relevant subsets of women with PrBC.

Changing the landscape of European School of Oncology-European Society for Medical Oncology masterclasses in clinical oncology during the COVID-19 pandemic.

Aims: This study aimed to assess the participants' evaluation of the European School of Oncology-European Society for Medical Oncology virtual masterclasses in clinical oncology (MCOs) organized during the pandemic in 2021. Materials & methods: The participants answered an online evaluation questionnaire at the end of each MCO to evaluate the content and organization of the MCO. Results: The clinical session and case presentation scores ranged between 4.6 and 4.8 over 5. The participants strongly agreed that the MCOs offered updates to improve their knowledge and practice in 68-83% and 52-76%, respectively; 74-90% of the participants considered the quality of the meetings to be excellent. Conclusion: The participants were satisfied with the virtual MCOs during the COVID-19 pandemic. Virtual MCO may be an acceptable alternative educational modality in specific circumstances.

In 2002, the European School of Oncology (ESO) established masterclasses in clinical oncology (MCOs) and provided 41 in-person courses over the past two decades. As the COVID-19 pandemic forced travel restrictions and social distancing, the ESO and the European Society for Medical Oncology (ESMO) adapted the traditional MCOs to create virtual MCOs presented on e-ESO, an ESO e-learning platform. To date, five virtual MCOs have been organized for oncologists from western Europe, Latin America, Arab countries and southern Europe, the Baltic and Eurasia, eastern Europe and the Balkans. This study aimed to assess the participants' evaluation of the ESO-ESMO virtual MCOs organized during the pandemic in 2021 and to compare the participants' evaluation with that of previous in-person MCOs conducted between 2002 and 2019.

Weekly Paclitaxel Administered During a Twin Pregnancy for Recurrent Breast Cancer: Case Report and Review of the Literature.

Although cancer treatment during single pregnancy has been standardized, how to manage cancer diagnosed during a multiple gestation is still unclear. Chemotherapy during pregnancy has shown to be safe, however, there are reports of increased risks of fetal complications such as intrauterine growth restriction and preterm birth. Also, how to best adjust this to the pharmacokinetic characteristics of a twin gestation has yet to be fully investigated. We report the case of an IVF twin pregnancy with a diagnosis of breast cancer recurrence shortly after conception, and how the pregnancy was managed to obtain optimal obstetric, maternal/oncological, and fetal outcomes.

ESO's career development program (2002-2021): Presentation and evaluation.

Over the last two decades, the European School of Oncology (ESO) provided a career development program to young oncologists by offering extensive learning programs. In 2020, the College of ESO was established to provide a fully comprehensive educational pathway that covers the different needs of medical students, oncology fellows and specialists. The following educational activities were organized worldwide: i) the masterclass in clinical oncology, ii) fellowships in clinical training centers, iii) the certificate of competence and advanced studies, iv) the medical student courses in oncology, v) the live e-sessions, vi) the refresher courses and vii) the Visiting Professor Program; and have reached areas where education is most needed and offered a variety of educational events in Europe, Eurasia, Middle East and Latin America. In this article, we present and evaluate the ESO educational programs devoted to young oncologists over the last 20 years.

Eight-Year Experience of the Certificate of Competence and Advanced Studies Program Organized by the European School of Oncology.

The Certificate of Competence and Advanced Studies Program is an academically recognized postgraduate program that is organized by the European School of Oncology in collaboration with the University of Ulm and the University of Zurich. It is a part-time educational activity that aims to provide physicians and scientists with advanced knowledge in the management of patients with breast cancer, lymphoma, and lung cancer. The program encloses three attendance seminars and four to five e-learning modules that extend over 12 to 14 months. To be certified, participants have to pass an online test after each module followed by a final certification exam at the end of the program. This article reports on the 8-year experience of the 166 graduated fellows who have attended the program.

The Contribution of the European School Of Oncology Education to the Central Asian and Caucasian Regions.

The European School of Oncology (ESO) organizes educational activities within Europe, the Mediterranean region, Central Asia, and the Caucasus. In this paper, we report on the participation of oncologists from Uzbekistan, Kazakhstan, Kirgizstan, Tajikistan, Azerbaijan, Georgia, and Armenia in various ESO activities including the masterclass, courses, refresher courses, conventions, conferences, consensus conferences, clinical training centers fellowship program, and the medical students' courses in oncology. Over the last 15 years, 428 oncologists and medical students have successfully attended one or more of the above activities organized in various European countries. This article details the implementation and coordination of the ESO educational events in the Central Asian and the Caucasian regions.

Early Breast Cancers During Pregnancy Treated With Breast-Conserving Surgery in the First Trimester of Gestation: A Feasibility Study.

Breast cancer is the most common malignancy occurring during gestation. In early-stage breast cancer during pregnancy (PrBC), breast-conserving surgery (BCS) with delayed RT is a rational alternative to mastectomy, for long considered the standard-of-care. Regrettably, no specific guidelines on the surgical management of these patients are available. In this study, we investigated the feasibility and safety of BCS during the first trimester of pregnancy in women with early-stage PrBC. All patients with a diagnosis of PrBC during the first trimester of pregnancy jointly managed in two PrBC-specialized Centers were included in this study. All patients underwent BCS followed by adjuvant radiotherapy to the ipsilateral breast after delivery. Histopathological features and biomarkers were first profiled on pre-surgical biopsies. The primary outcome was the isolated local recurrence (ILR). Among 168 PrBC patients, 67 (39.9%) were diagnosed during the first trimester of gestation. Of these, 30 patients (age range, 23-43 years; median=36 years; gestational age, 2-12 weeks; median=7 weeks; median follow-up time=6.5 years) met the inclusion criteria. The patients that were subjected to radical surgery (n=14) served as controls. None of the patients experienced perioperative surgical complications. No ILR were observed within three months (n=30), 1 year (n=27), and 5 years (n=18) after surgery. Among the study group, 4 (12.3%) patients experienced ILR or new carcinomas after 6-13 years, the same number (n=4) had metastatic dissemination after 3-7 years. These patients are still alive and disease-free after 14-17 years of follow-up. The rate of recurrences and metastasis in the controls were not significantly different. The findings provide evidence that BCS in the first trimester PrBC is feasible and reasonably safe for both the mother and the baby.

Who are the women who enrolled in the POSITIVE trial: A global study to support young hormone receptor positive breast cancer survivors desiring pregnancy.

BACKGROUND: Premenopausal women with early hormone-receptor positive (HR+) breast cancer receive 5-10 years of adjuvant endocrine therapy (ET) during which pregnancy is contraindicated and fertility may wane. The POSITIVE study investigates the impact of temporary ET interruption to allow pregnancy. METHODS: POSITIVE enrolled women with stage I-III HR + early breast cancer, ≤42 years, who had received 18-30 months of adjuvant ET and wished to interrupt ET for pregnancy. Treatment interruption for up to 2 years was permitted to allow pregnancy, delivery and breastfeeding, followed by ET resumption to complete the planned duration. FINDINGS: From 12/2014 to 12/2019, 518 women were enrolled at 116 institutions/20 countries/4 continents. At enrolment, the median age was 37 years and 74.9 % were nulliparous. Fertility preservation was used by 51.5 % of women. 93.2 % of patients had stage I/II disease, 66.0 % were node-negative, 54.7 % had breast conserving surgery, 61.9 % had received neo/adjuvant chemotherapy. Tamoxifen alone was the most prescribed ET (41.8 %), followed by tamoxifen + ovarian function suppression (OFS) (35.4 %). A greater proportion of North American women were <35 years at enrolment (42.7 %), had mastectomy (59.0 %) and received tamoxifen alone (59.8 %). More Asian women were nulliparous (81.0 %), had node-negative disease (76.2%) and received tamoxifen + OFS (56.0 %). More European women had received chemotherapy (69.3 %). INTERPRETATION: The characteristics of participants in the POSITIVE study provide insights to which patients and doctors considered it acceptable to interrupt ET to pursue pregnancy. Similarities and variations from a regional, sociodemographic, disease and treatment standpoint suggest specific sociocultural attitudes across the world.

Pregnancy After Breast Cancer: A Systematic Review and Meta-Analysis.

PURPOSE: Many patients and physicians remain concerned about the potential detrimental effects of pregnancy after breast cancer (BC) in terms of reproductive outcomes and maternal safety. This systematic review and meta-analysis aimed at providing updated evidence on these topics. METHODS: A systematic literature review was conducted to identify studies including patients with a pregnancy after BC (PROSPERO number CRD42020158324). Likelihood of pregnancy after BC, their reproductive outcomes, and maternal safety were assessed. Pooled relative risks, odds ratios (ORs), and hazard ratios (HRs) with 95% CIs were calculated using random effects models. RESULTS: Of 6,462 identified records, 39 were included involving 8,093,401 women from the general population and 112,840 patients with BC of whom 7,505 had a pregnancy after diagnosis. BC survivors were significantly less likely to have a subsequent pregnancy compared with the general population (relative risk, 0.40; 95% CI, 0.32 to 0.49). Risks of caesarean section (OR, 1.14; 95% CI, 1.04 to 1.25), low birth weight (OR, 1.50; 95% CI, 1.31 to 1.73), preterm birth (OR, 1.45; 95% CI, 1.11 to 1.88), and small for gestational age (OR, 1.16; 95% CI, 1.01 to 1.33) were significantly higher in BC survivors, particularly in those with previous chemotherapy exposure, compared with the general population. No significantly increased risk of congenital abnormalities or other reproductive complications were observed. Compared to patients with BC without subsequent pregnancy, those with a pregnancy had better disease-free survival (HR, 0.66; 95% CI, 0.49 to 0.89) and overall survival (HR, 0.56; 95% CI, 0.45 to 0.68). Similar results were observed after correcting for potential confounders and irrespective of patient, tumor, and treatment characteristics, pregnancy outcome, and timing of pregnancy. CONCLUSION: These results provide reassuring evidence on the safety of conceiving in BC survivors. Patients' pregnancy desire should be considered a crucial component of their survivorship care plan.

Breast cancer diagnosed in the post-weaning period is indicative for a poor outcome.

BACKGROUND: In young women, a breast cancer diagnosis after childbirth increases the risk for metastasis and death. Studies in rodents suggest that post-weaning mammary gland involution contributes to the poor prognosis of postpartum breast cancers. However, this association has not been investigated in humans, mainly because of missing information on the patient's lactation status at diagnosis. PATIENTS AND METHODS: Clinicopathological data of 1180 young women with primary invasive breast cancer, diagnosed within 2 years postpartum (PP-BC), during pregnancy (Pr-BC), or nulliparous (NP-BC), were collected. For PP-BC patients, breastfeeding history was retrieved to differentiate breast cancers identified during lactation (PP-BCDL) from those diagnosed post-weaning (PP-BCPW). Differences in prognostic parameters, first site of distant metastasis, and risks for metastasis and death were determined between patient groups. RESULTS: Cox proportional hazard models pointed to a twofold increased the risk of metastasis and death in PP-BCPW patients compared with PP-BCDL (hazard ratio [HR] 2.1 [PDRS = 0.021] and 2.9 [POS = 0.004]), Pr-BC (HR 2.1 [PDRS<0.001] and 2.3 [POS<0.001]) and NP-BC (HR 2.1 [PDRS<0.001] and 2.0 [POS<0.001]) patients. Prognosis was poorest for PP-BCPW patients who did not breastfeed or only for ≤ 3 months before diagnosis. This could not fully be attributed to differences in standard prognostic characteristics. In addition, PP-BCPW tumours showed a 3- to 8-fold increased risk to metastasise to the liver, yet this did not correlate with the poor outcome of this patient cohort. CONCLUSIONS: Breast cancer diagnosed shortly after weaning specifically adds to the poor prognosis in women diagnosed with PP-BC. Apart from the importance of an increased awareness, these data show that detailed lactation data need to be registered when breast cancer outcome in young women is investigated.