Association of DCIS size and margin status with risk of developing breast cancer post-treatment: multinational, pooled cohort study

OBJECTIVE

To examine the association between size and margin status of ductal carcinoma in situ (DCIS) and risk of developing ipsilateral invasive breast cancer and ipsilateral DCIS after treatment, and stage and subtype of ipsilateral invasive breast cancer.

DESIGN

Multinational, pooled cohort study.

SETTING

Four large international cohorts.

PARTICIPANTS

Patient level data on 47 695 women with a diagnosis of pure, primary DCIS between 1999 and 2017 in the Netherlands, UK, and US who underwent surgery, either breast conserving or mastectomy, often followed by radiotherapy or endocrine treatment, or both.

MAIN OUTCOME MEASURES

The main outcomes were 10 year cumulative incidence of ipsilateral invasive breast cancer and ipsilateral DCIS estimated in relation to DCIS size and margin status, and adjusted hazard ratios and 95% confidence intervals, estimated using multivariable Cox proportional hazards analyses with multiple imputed data RESULTS: The 10 year cumulative incidence of ipsilateral invasive breast cancer was 3.2%. In women who underwent breast conserving surgery with or without radiotherapy, only adjusted risks for ipsilateral DCIS were significantly increased for larger DCIS (20-49 mm) compared with DCIS <20 mm (hazard ratio 1.38, 95% confidence interval 1.11 to 1.72). Risks for both ipsilateral invasive breast cancer and ipsilateral DCIS were significantly higher with involved compared with clear margins (invasive breast cancer 1.40, 1.07 to 1.83; DCIS 1.39, 1.04 to 1.87). Use of adjuvant endocrine treatment was not significantly associated with a lower risk of ipsilateral invasive breast cancer compared to treatment with breast conserving surgery only (0.86, 0.62 to 1.21). In women who received breast conserving treatment with or without radiotherapy, higher DCIS grade was not significantly associated with ipsilateral invasive breast cancer, only with a higher risk of ipsilateral DCIS (grade 1: 1.42, 1.08 to 1.87; grade 3: 2.17, 1.66 to 2.83). Higher age at diagnosis was associated with lower risk (per year) of ipsilateral DCIS (0.98, 0.97 to 0.99) but not ipsilateral invasive breast cancer (1.00, 0.99 to 1.00). Women with large DCIS (≥50 mm) more often developed stage III and IV ipsilateral invasive breast cancer compared to women with DCIS <20 mm. No such association was found between involved margins and higher stage of ipsilateral invasive breast cancer. Associations between larger DCIS and hormone receptor negative and human epidermal growth factor receptor 2 positive ipsilateral invasive breast cancer and involved margins and hormone receptor negative ipsilateral invasive breast cancer were found.

CONCLUSIONS

The association of DCIS size and margin status with ipsilateral invasive breast cancer and ipsilateral DCIS was small. When these two factors were added to other known risk factors in multivariable models, clinicopathological risk factors alone were found to be limited in discriminating between low and high risk DCIS.

DCIS and LCIS: Are the Risk Factors for Developing In Situ Breast Cancer Different?

Ductal carcinoma in situ (DCIS) is widely accepted as a precursor of invasive ductal carcinoma (IDC). Lobular carcinoma in situ (LCIS) is considered a risk factor for invasive lobular carcinoma (ILC), and it is unclear whether LCIS is also a precursor. Therefore, it would be expected that similar risk factors predispose to both DCIS and IDC, but not necessarily LCIS and ILC. This study examined associations with risk factors using data from 3075 DCIS cases, 338 LCIS cases, and 1584 controls aged 35-60, recruited from the UK-based GLACIER and ICICLE case-control studies between 2007 and 2012. Analysis showed that breastfeeding in parous women was protective against DCIS and LCIS, which is consistent with research on invasive breast cancer (IBC). Additionally, long-term use of HRT in post-menopausal women increased the risk of DCIS and LCIS, with a stronger association in LCIS, similar to the association with ILC. Contrary to findings with IBC, parity and the number of births were not protective against DCIS or LCIS, while oral contraceptives showed an unexpected protective effect. These findings suggest both similarities and differences in risk factors for DCIS and LCIS compared to IBC and that there may be justification for increased breast surveillance in post-menopausal women taking long-term HRT.

Abstract P6-03-05: Clinico-pathological co-variates define a predictive model of breast cancer related lymphoedema (BCRL) in patients undergoing axillary surgery for breast cancer

Clinico-pathological co-variates define a predictive model of breast cancer related lymphoedema (BCRL) in patients undergoing axillary surgery for breast cancer CC Tang1*, J Timbres2*, KWD Ramsey1, A Mera2, S Irshad2, E Sawyer2, AA Khan1 1 Department of Plastic Surgery, The Royal Marsden Hospital, London, UK 2 School of Cancer and Pharmaceutical Sciences, Faculty of Life Sciences and Medicine, Guy’s Cancer Centre, King’s College London, London, UK. *These authors contributed equally Introduction Breast cancer-related lymphoedema (BCRL) negatively impacts body image, limb function and quality-of-life during cancer survivorship and affects 20% of women undergoing axillary clearance (ALND).1 Stratifying women undergoing axillary intervention into high- and low-risk groups for BCRL is important to identify those most likely to benefit from surgical interventions for lymphoedema prevention (eg LYMPHA) and mitigate BCRL risk in this subset of patients. In this study, we aimed to identify prognostic factors for lymphoedema incidence to develop a more accurate model of BCRL risk. Methods We performed a retrospective cohort study of breast cancer patients undergoing axillary surgery with (Ly+) and without (Ly-) subsequent lymphoedema. Controls were identified from the Breast Cancer Clinical Database, Guy’s and St Thomas’ Hospital NHS Foundation Trust (GSTT)) and diagnosed between 2000-2016, while cases were identified from the Lymphoedema Clinic at GSTT, diagnosed between 2000-2020. A multivariate logistic regression model was derived from univariate analyses using a stepwise, iterative process, confirmed with lasso regression, and evaluated within training and validation datasets to define a predictive risk score using methods described by Pavlou et al.2 Results 2040 patients (Ly+=541, Ly-=1499) who underwent axillary surgery (ALND = 1171, SLNB = 755) (were included in our analysis with a median follow up of 7.2 years (Ly+) and 9.8 years (Ly-). The final predictive model of BCRL risk contained variables for: mastectomy, grade, T-stage, N-stage, ER status, chemotherapy and radiotherapy. Here, specifically radiotherapy including a supraclavicular fossa field was associated with developing lymphoedema. The Hosmer–Lemeshow goodness-of-fit test showed the model to be well calibrated, and evaluation of the risk score using ROC curves showed good discrimination (AUC: 0.795). Lymphoedema was not found to negatively affect overall (unadjusted HR: 1.19 (95% CI: 0.92-1.53); p=0.178 and adjusted HR: 0.53 (95% CI: 0.38-0.73); p&lt; 0.001) or disease free (unadjusted HR: 2.03 (95% CI: 1.59-2.61); p&lt; 0.001 and adjusted HR: 0.92 (95% CI: 0.68-1.23); p=0.57) survival. Conclusion Our study identified clinico-pathological factors such as mastectomy, grade, T-stage, N-stage, ER status, chemo- and radiotherapy (specifically radiotherapy including a supraclavicular fossa field) to be predictive of developing BCRL following axillary surgery. Our model requires further validation but may have utility in stratifying patients for whom surgical strategies for lymphoedema prevention could be deployed to mitigate BCRL risk. References 1. DiSipio T, Rye S, Newman B, Hayes S. Incidence of unilateral arm lymphoedema after breast cancer: a systematic review and meta-analysis. Lancet Oncol. 2013 May;14(6):500-15. doi: 10.1016/S1470-2045(13)70076-7. Epub 2013 Mar 27. PMID: 23540561. 2. Pavlou M, Ambler G, Seaman S R, Guttmann O, Elliott P, King M et al. How to develop a more accurate risk prediction model when there are few events BMJ 2015; 351 :h3868 doi:10.1136/bmj.h3868

Citation Format: Chee Chee Tang, Jasmine Timbres, Kelvin Ramsey, Anca Mera, Sheeba Irshad, Elinor Sawyer, Aadil Khan. Clinico-pathological co-variates define a predictive model of breast cancer related lymphoedema (BCRL) in patients undergoing axillary surgery for breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-03-05.

Abstract 686: Subsequent invasive breast cancer risk after DCIS treatment in multinational PRECISION consortium cohorts comprising 48,576 patients

Background: Although DCIS is a precursor of invasive breast cancer (IBC), most DCIS lesions never will progress. As we cannot distinguish reliably progressive from harmless DCIS yet, almost all women with DCIS are treated extensively with surgery and often adjuvant radiotherapy or endocrine treatment, implying overtreatment of many thousands of women with harmless DCIS. PRECISION aims to reduce such overtreatment by identifying factors associated with subsequent ipsilateral IBC. Many factors have been implicated in subsequent DCIS and IBC risk, but most studies relied on small series with limited prognostic power. To overcome this, we conducted pooled analyses of four large cohorts with DCIS from three different countries.

Methods: Cohorts were pooled with data of 48,804 women with DCIS: a population-based cohort (NL, n=18,996), prospective, a population-based, screening cohort (Sloane, UK, n=8,462), a single center cohort (MDACC, USA, n=2,363), and a representative DCIS patient series from the National Cancer Database Special Study (USA, n=18,983). Patients with missing data on treatment and follow-up or follow-up shorter than six months were excluded from analyses. Risk of a subsequent ipsilateral invasive breast cancer (iIBC) was assessed in three DCIS lesion size groups (&lt;20mm, 20-50mm and ≥50mm) and in patients who had clear surgical margins (&lt;2mm) after final breast conserving surgery (BCS) versus patients who did not. Cox proportional hazards models were used to assess differences in risk of IBC, with a focus on DCIS size and margin status.

Results: In final analyses, 48,576 patients, diagnosed between 1999 and 2017, were included. Median follow-up was 7.6 years (range 0.5-21.1). In multivariable analyses, patients with smaller size of DCIS (&lt;20mm) had a decreased risk of iIBC compared with women with larger lesion size (HR 0.81; 95% CI 0.68-0.97). In 33,091 BCS treated patients, patients with clear surgical margins had a decreased risk of iIBC (HR 0.68; 95% CI 0.52-0.90).

Conclusion: In our quest to reduce overtreatment for women with DCIS, we have identified free surgical margins and smaller lesion size as independent factors reducing the risk of subsequent ipsilateral invasive breast cancer, irrespective of the treatment received. Knowledge of these, and additional, factors could aid in selecting patients suitable for less invasive management strategies such as active surveillance or omitting radiotherapy. This work was supported by Cancer Research UK and by KWF Dutch Cancer Society (ref.C38317/A24043); Web site: https://cancergrandchallenges.org/teams/precision

Citation Format: Renee S. Schmitz, Alexandra W. van den Belt-Dusebout, Karen Clements, Yi Ren, Chiara Cresta, Jasmine Timbres, Yat-Hee Liu, Danalyn Byng, Thomas Lynch, Brian Menegaz, Deborah Collyar, Terry Hyslop, Michael Schaapveld, Elinor Sawyer, Shelley E. Hwang, Alastair Thompson, Marc D. Ryser, Jelle Wesseling, Esther H. Lips, Marjanka K. Schmidt, Grand Challenge PRECISION Consortium. Subsequent invasive breast cancer risk after DCIS treatment in multinational PRECISION consortium cohorts comprising 48,576 patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 686.

Abstract P1-22-02: Subsequent risk of ipsilateral breast events in a multinational DCIS cohort of 48.619 patients: A meta-analysis within the PRECISION consortium

Background: The PRECISION (PREvent ductal Carcinoma In Situ Invasive Overtreatment Now) CRUK Grand Challenge project focusses on discriminating hazardous from indolent ductal carcinoma in situ (DCIS). Aim of these analyses is to identify factors associated with a lower or higher risk of developing invasive breast cancer after an initial DCIS diagnosis. Knowledge of these factors is crucial in our quest to reducing overtreatment for women with DCIS. Many clinicopathological features are hypothesized to be important factors affecting the risk of a subsequent breast lesion. Most studies performed so far are from trial or single country studies, we now present an integrated analysis of four different cohorts from three countries.Methods: Four cohorts from the three countries participating in PRECISION were identified. A population based cohort from the Netherlands cancer registry (Dutch cohort); a population based, prospective, screening cohort from the United Kingdom (Sloane cohort); a single center cohort from MD Anderson Cancer Center (MDACC) and a subset of DCIS patients abstracted from a population based National Cancer Database Special Study cohort (NCDB subset) in the United States. Patient-level data from these cohorts were combined for this analysis. Subsequent ipsilateral invasive breast cancer (iIBC) and subsequent ipsilateral DCIS (iDCIS) were assessed at five and ten years by Kaplan Meier analysis. The cumulative incidence of iIBC was assessed in three treatment groups: breast conserving surgery only (BCS), breast conserving surgery with radiotherapy (BCS+RT) and mastectomy (MST). Cumulative incidence of iDCIS was assessed in patients receiving BCS or BCS+RT. Additionally, cumulative incidences were calculated for iIBC and IDCIS in patients who received endocrine treatment (ET) after BCS or BCS+RT versus patients who did not receive ET. All cumulative incidences were calculated with death as competing risk. Results: The joint PRECISION cohort consisted of 48,619 patients, diagnosed between 1999 and 2017. Median follow-up was 7.4 years (0.6-17.9). In preliminary analyses, Kaplan Meier curves showed broadly similar risks in iIBC and iDCIS between the four different cohorts. The cumulative incidence of iIBC was 1.6% at five years and 3.5% at 10 years. Five-year cumulative incidence of iIBC was highest in patients receiving BCS (3.4%) compared with patients receiving BCS+RT or MST (1.3%). The cumulative incidence of iDCIS was 1.7% at 5 years and 2.4% at 10 years. Five-year cumulative incidence of iDCIS was higher in patients receiving BCS (3.5%) compared to patients receiving BCS+RT (1.9%). In univariate analyses, the effect of ET on cumulative incidence of both iIBC and iDCIS was modest, especially with respect to radiotherapy. Conclusion: Overall, 5- and 10-year incidence of an ipsilateral in situ or invasive breast lesion was low and similar between the four different cohorts. The incidence of iIBC and iDCIS was higher in patients receiving BCS, compared to women receiving BCS+RT or MST.

Table 1.Cohort and patient characteristicsDutch Cohort Sloane MDACCNCDB subsetTotal CohortN=18,995N=8,425N=1,820N=19,379N=48,619Cohort descriptionProspectiveNoYesNoNoPopulation basedYesYesNo, single centerYesScreening and non-screeningYesScreening onlyYesYesMean (min - max)Mean (min - max)Mean (min - max)Mean (min-max)Mean (min-max)Age diagnosis DCIS58.3 (21-94)59.8 (46-88)55.6 (20-90)59.7 (20-98)59.0 (20-98)Year of diagnosis (range)1999-20152003-20121999-20172007-20151999-2017Follow-up in years10.4 (0.5-21.1)5.3 (0.5-9.7)8.7 (0.25-17.8)5.8 (0.5-10.7)7.6 (0.25-2.1)N (%)N (%)N (%)N (%)N (%)GradeGrade 12,844 (15.0)784 (9.3)141 (7.8)3,158 (16.3)6,927 (14.3)Grade 25,952 (31.3)2,328 (27.6)737 (40.5)6,844 (35.3)15,861 (32.6)Grade 38,944 (47.1)5,305 (62.9)933 (51.3)7,848 (40.5)23,030 (47.3)Unknown grade1,255 (6.6)8 (0.1)9 (0.5)1,529 (7.9)2,801 (5.8)Type of surgeryBreast conserving surgery (BCS)11,790 (62.1)5,830 (69.2)1,031 (56.7)14,504 (74.8)33,155 (68.2)Mastectomy (MST)7,205 (37.9)2,595 (30.8)789 (43.4)4,875 (25.2)15,464 (31.8)Adjuvant treatmentRadiotherapy (RT)9,650 (50.8)3,418 (40.6)762 (41.9)10,620 (54.8)24,450 (50.3)Endocrine treatmentNA1,151 (13.6)999 (54.9)8,849 (45.7)10,999 (37.0)5 years Cumulative IncidencesiIBC1.4%2.3%1.6%1.7%1.6%iDCIS1.5%2.0%1.6%1.7%1.7%Vital statusAlive16,472 (86.7)8,147 (96.7)1,668 (91.7)18,161 (93.7)44,448 (91.4)Deceased2,523 (13.3)278 (3.3)152 (8.4)1,218 (6.3)4,171 (8.6)This work was supported by Cancer Research UK and by KWF Dutch Cancer Society (ref.C38317/A24043)

Citation Format: Renée SJM Schmitz, Sandra W van den Belt-Dusebout, Chiara Cresta, Yat-Hee Liu, Michael Schaapveld, Karen Clements, Jasmine Timbres, Danalyn T Byng, Marc D Ryser, Yi Ren, Thomas Lynch, Terry Hyslop, Brian Menegaz, Deborah Collyar, Shelley Hwang, Alastair Thompson, Elinor Sawyer, Jelle Wesseling, Esther H Lips, Marjanka K Schmidt, Grand Challenge PRECISION consortium. Subsequent risk of ipsilateral breast events in a multinational DCIS cohort of 48.619 patients: A meta-analysis within the PRECISION consortium [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-22-02.

Survival Outcomes in Invasive Lobular Carcinoma Compared to Oestrogen Receptor-Positive Invasive Ductal Carcinoma

Invasive lobular breast cancer (ILC) accounts for 10-15% of breast cancers and has distinct characteristics compared with the more common invasive ductal carcinoma (IDC). Studies have shown that ILC may be less sensitive to chemotherapy than IDC, with lower rates of complete pathological response after neo-adjuvant chemotherapy, but it is not clear how this affects long-term survival. Patients at Guy's and St Thomas' NHS Foundation Trust between 1975 and 2016 diagnosed with ER+ IDC or ER+ ILC were eligible for inclusion. Kaplan-Meier plots and Cox proportional-hazards regression models were used for analysis. There was no difference in overall survival comparing ER+ ILC to ER+ IDC (OR: 0.94, 95% CI: 0.83, 1.04) with a median follow-up time of 8.3 years compared to 8.4 years in IDC. However, ER+HER2- ILC had worse survival compared to ER+HER2- IDC in those that received chemotherapy (OR: 1.46, 95% CI: 1.06, 2.01). Here, median follow-up time was 7.0 years in ILC compared to 8.1 years in IDC. These results indicate worse overall survival after chemotherapy (neo-adjuvant and adjuvant) in ILC compared to ER+HER2- IDC even when correcting for tumour grade, age, size, and nodal involvement, but validation is needed in a larger study population.

Abstract PS8-06: Survival outcomes after chemotherapy in invasive lobular carcinoma compared to estrogen receptor positive invasive ductal carcinoma

Introduction

Invasive lobular breast cancer (ILC) accounts for 10-15% of all invasive breast carcinomas and has distinct clinical and biological characteristics compared with the more common invasive ductal carcinoma (IDC). They are generally ER-positive (ER+) with the exception of a small number of pleomorphic cases and there is some evidence that the 10-year survival rate of women with ILC is lower than that for ER+ IDC. Furthermore, studies have shown that ILC may be less sensitive to chemotherapy than IDC, with lower rates of complete pathological response after neoadjuvant chemotherapy, but it is not clear what effects this has on long term survival. The aim of this study was to investigate whether ER+ ILC patients who received chemotherapy (neoadjuvant or adjuvant) had similar outcomes to ER+ IDC patients who received chemotherapy.

Methods

Patients were diagnosed at Guy’s & St Thomas’ NHS Foundation Trust between 1971 and 2016 and were eligible for inclusion into the study if they were female, had been diagnosed with either IDC or ILC, if their tumours were ER+, and if they received chemotherapy. They were followed up from date of primary diagnosis until 30th June 2019 and were assumed to be alive in the absence of a reported death date. Patients with estrogen receptor negative (ER-) tumours were excluded, due to well-known chemosensitivity in these breast cancer subtypes. Data used was requested from the Guy’s & St Thomas’ Breast Cancer Database.

Results

Of 5526 patients diagnosed with ILC or IDC between 1971 and 2016, 3945 were ER+ with 3436 IDC and 509 ILC. ER+ IDC and ILC had similar survival for the first 10 years after diagnosis after which outcomes began to diverge with worse outcomes in ILC. The 10-year and 15-year survival of 59.3% and 47.5% respectively were seen in IDC, and 58.6% and 44.6% in ILC. 1327 ER+ patients who received chemotherapy were selected for analysis, of which 161 (12.1%) were ILC and 1166 (87.9%) were IDC. 159 (12.0%) of patients received neo-adjuvant chemotherapy, while 1168 (88.0%) received adjuvant chemotherapy. In chemotherapy patients, 10-year survival was 53.1% in ILC and 54.0% in IDC, and by 15 years this was 35.1% and 44.7% respectively. In ER+ chemotherapy patients, there was no evidence of a crude association between histological subtype and survival (HR: 1.19, 95% CI: 0.97, 1.47) using Cox regression. However, the multivariate Cox regression model estimated a significantly worse outcome in ILC compared to IDC (HR: 1.28, 95% CI: 1.02, 1.60), adjusted for chemotherapy (neo-adjuvant or adjuvant), stage (I-IV), grade, HER2 status, time period of diagnosis, and surgery type (mastectomy or excision). When stratified by chemotherapy, this association was only observed in patients that received adjuvant treatment.

Conclusion

This study suggests that ER+ ILC patients who received adjuvant chemotherapy may have a worse outcome than ER+ IDC when adjusted for stage and grade. This is a potentially important finding but needs to be studied in a larger population treated with modern chemotherapy regimens. Other studies have shown that the outcome for ILC is better in the first 5 years after diagnosis compared to ER+ IDC but worsens after 10 years, as it does in this study. Thus, having long follow up is essential in order to be able to detect any differences in survival between ILC and ER+ IDC. Nonetheless, this study has displayed a significant difference in survival between ER+ ILC and ER+ IDC receiving adjuvant chemotherapy, and thus recommendations for adjuvant chemotherapy may need to be considered separately for the two subtypes. Furthermore, it would be beneficial to develop a tool that could help in identifying cases of ILC that would most benefit from chemotherapy.

Citation Format: Jasmine Timbres, Charlotte Moss, Anca Mera, Anna Haire, Cheryl Gillett, Mieke Van Hemelrijck, Elinor Sawyer. Survival outcomes after chemotherapy in invasive lobular carcinoma compared to estrogen receptor positive invasive ductal carcinoma [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-06.

Abstract PS7-83: Outcomes and risk factors associated with breast cancer in women aged 35 and under: Single centre retrospective analysis

Introduction Breast cancer is the most common malignancy affecting women under the age of 35 and young age at diagnosis is associated with a poor prognosis. Previous studies have shown that these patients have adverse tumour biology including high grade morphology, lymph node involvement and lack of hormone receptor expression. The aim of this study was to assess the outcomes and risk factors associated with the different subtypes of breast cancer as defined by receptor status in a cohort of young patients in a central London cancer centre. Methods Women diagnosed with breast cancer at the age of 35 or younger between 1st January 2010 and 1st June 2020, at Guys and St Thomas’ NHS Foundation Trust (GSTT) were identified from the GSTT Breast Cancer Clinical Database. Data on patient demographics, histopathology, treatment, family history of breast or ovarian cancer, recent use of oral contraceptive pill (OCP) and outcome were collected from electronic hospital records. Risk factor data was analysed using chi-squared (χ2) statistical analysis; survival data (Overall survival (OS) and recurrence free survival (RFS)) was assessed using cox-regression analysis and formulation of Kaplan-Meier curves. Results We identified 119 patients with a median age of 32.5 years (range 22-35 years). Four were diagnosed with in situ carcinoma (3 DCIS, 1 LCIS) and the remainder were invasive cancers. Of the invasive cancers, 54% (n= 62) were ER+HER2-, 23% (n=26) ER-HER2-, 19% (n=22) ER+HER2+ and 4% (n=5) ER-HER2+. The majority of patients presented with stage 1 or 2 disease and a small number presented with metastatic disease, irrespective of subtype. Approximately 23% (n= 28) of patients had taken the OCP and 15% (n=18) of patients were pregnant or breast feeding at the time of diagnosis, with no variation by subtype. ER+HER2+ patients were less likely to have had children (p=0.0008). ER+HER2- patients were more likely than ER-HER2- patients to have a family history of breast cancer (P=0.03), but were less likely to be referred for genetic testing (52% (n=38) vs 81% (n=21)). 11.8% (n=14) were found to have a germline mutation, two occurred with in situ cancer (BRCA2 in the case of LCIS and TP53 in a case of ER+HER2+ DCIS). Of the ER+HER2- cases that underwent genetic testing 12.5% (n=4) had a germline mutation (2 BRCA2, 1 PALB2, 1 CHEK2) and 38% (n=8) of the ER-HER2-subgroup (6 BRCA1, 2 BRCA2). With a median follow up of 29 months (range 3.1 to 103.3 months), 23% of ER-HER2-, 10% of ER+HER2- and no HER2+ cases had developed a recurrence (loco-regional or distant). 5-year RFS in ER+HER2- was 79.5% vs. 61.9% in ER-HER2- (HR 2.96, 95%CI 0.95-9.20; p=0.061). Of the ER+HER2- patients that recurred, 83% (n=5) had full ovarian function suppression (OFS) with Goserelin. Mean survival was 36.4 months; 12 out of 115 patients died, the 5-year OS across all subgroups was 76.7%. ER-HER2- patients were more likely to have died (27% (n=7) (HR 5.9 95%CI 1.69-20.46; p=0.005), with a 5-year OS of only 47%. Only 6% (n=4) of ER+HER2- patients died, they had a 5-year OS of 89.3%. Only 5% (n=1) of ER+HER2+ patients died (HR 1.47 95%CI 0.16-13.80; p=0.733) with a 5-year OS of 75%. Conclusions Despite optimum treatment, 23% of women under 35 with ER-HER2- breast cancer still died from their disease. In addition, even with this relatively short follow up, there is a subgroup of ER+HER2- patients who presented with a low nodal burden, were treated with full OFS and still recurred. This group of patients would benefit from somatic molecular testing to identify potential treatment targets. The majority of HER2+ patients in this cohort also had ER+ disease which is similar to previous reports of HER2+ breast cancer in young women. However contrary to that report, HER2+ positive patients in our study had a low risk of recurrence, this is likely due to the widespread use of targeted anti-HER2 therapy.

Citation Format: Joanna Dodkins, Elizabeth Harvey-Jones, Sameer Sengupta, Jasmine Timbres, Angela Swampillai, Elinor Sawyer. Outcomes and risk factors associated with breast cancer in women aged 35 and under: Single centre retrospective analysis [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-83.