Validity and Efficiency of Progression-Free Survival-2 as a Surrogate End Point for Overall Survival in Advanced Cancer Randomized Trials

PURPOSE

Progression-free survival (PFS)-2, defined as the time from randomization to progression on second-line therapy, is potentially a more reliable surrogate than PFS for overall survival (OS), but will require longer follow-up and a larger sample size. We sought to compare the validity and efficiency, defined as proportional increase in follow-up time and sample size, of PFS-2 to PFS.

METHODS

We performed an electronic search to identify randomized trials of advanced solid tumors reporting PFS, PFS-2, and OS as prespecified end points. Only studies that had protocols that defined measurement of PFS-2 and follow-up for patients after first disease progression were included. We compared correlations in the relative treatment effect for OS with PFS and PFS-2. We reconstructed individual patient data from survival curves to estimate time to statistical significance (TSS) of the relative treatment effect. We further computed the sample size (person-year [PY] follow-up) required to reach statistical significance.

RESULTS

Across the 42 analysis units and 21,255 patients, the correlation of the relative treatment effect between OS and PFS-2, r, was 0.70 (95% CI, 0.41 to 0.80) and r = 0.46 (95% CI, 0.26 to 0.74) for OS and PFS. The median differences in TSS between OS with PFS, OS with PFS-2, and PFS with PFS-2 were 16.59 (95% CI, 4.48 to not reached [NR]), 10.0 (95% CI, 2.2 to NR), and 4.31 (95% CI, 2.92 to 13.13) months, respectively. The median difference in PYs required to reach statistical significance for PFS-2 over PFS was 156 (95% CI, 82 to 500) PYs, equivalent to an estimated median 12.7% increase in PYs.

CONCLUSION

PFS-2 offers improved correlation with OS than PFS with a modest increase in follow-up time and sample size. PFS-2 should be considered as a primary end point in future trials of advanced cancers.

Reduced number of admissions with acute appendicitis but not severe acute appendicitis at two Sydney hospitals during the first COVID-19 lockdown period

Background

This study investigated whether there was a change in acute appendicitis, appendicectomy admissions or disease severity during the 2020 lockdown period in NSW.

Methods

A retrospective before‐and‐after study was undertaken of patients admitted to two Sydney hospitals (St. Vincent's and Liverpool Hospitals) who had appendicectomy for presumed acute appendicitis and patients who had confirmed appendicitis but did not undergo surgery. Study periods were the 2020 lockdown period (15 March–15 May 2020), the corresponding period in the previous year, and the 1‐month after these periods. Patients were classified as having no, mild or severe appendicitis using operation and histopathological reports.

Results

(Thirty‐six percent) fewer patients were admitted with acute appendicitis during the lockdown period compared with the previous year with a substantial reduction in normal/mild appendicitis presentations (OR 0.56, 95% CI 0.34–0.93, P = 0.03). There were 46% fewer patients with mild appendicitis during lockdown (56) compared with the previous year (103); numbers of patients with severe appendicitis were very similar (46 vs. 51). There was no increase in number of admissions with severe appendicitis, or in the time from onset of symptoms to admission, in the month following lockdown.

Conclusion

Compared with the previous year, there were markedly fewer admissions with appendicitis during lockdown, with no evidence of a shift to more cases of severe appendicitis nor delayed presentation in the post‐lockdown period. It is plausible that some patients with mild appendicitis may have recovered without hospitalization, supporting the importance of implementing trials on non‐surgical management of appendicitis.

During COVID‐19 lockdown in Sydney we noted a reduction in hospital presentations with acute appendicitis but not severe acute appendicitis. Mild appendicitis may be able to be successfully managed in the outpatient setting.

De novo and recurrent metastatic breast cancer - A systematic review of population-level changes in survival since 1995

BACKGROUND

Advances in breast cancer (BC) care have reduced mortality, but their impact on survival once diagnosed with metastasis is less well described. This systematic review aimed to describe population-level survival since 1995 for de novo metastatic BC (dnMBC) and recurrent MBC (rMBC).

METHODS

We searched MEDLINE 01/01/1995-12/04/2021 to identify population-based cohort studies of MBC reporting overall (OS) or BC-specific survival (BCSS) over time. We appraised risk-of-bias and summarised survival descriptively for MBC diagnoses in 5-year periods from 1995 until 2014; and for age, hormone receptor and HER2 subgroups.

FINDINGS

We identified 20 eligible studies (14 dnMBC, 1 rMBC, 5 combined). Potential sources of bias in these studies were confounding and shorter follow-up for the latest diagnosis period.For dnMBC, 13 of 14 studies reported improved OS or BCSS since 1995. In 2005-2009, the median OS was 26 months (range 24-30), a median gain of 6 months since 1995-1999 (range 0-9, 4 studies). Median 5-year OS was 23% in 2005-2009, a median gain of 7% since 1995-1999 (range -2 to 14%, 4 studies). For women ≥70 years, the median and 5-year OS was unchanged (1 study) with no to modest difference in relative survival (range: -1·9% (p = 0.71) to +2·1% (p = 0.045), 3 studies). For rMBC, one study reported no change in survival between 1998 and 2006 and 2007-2013 (median OS 23 months). For combined MBC, 76-89% had rMBC. Three of four studies observed no change in median OS after 2000. Of these, one study reported median OS improved for women ≤60 years (1995-1999 19·1; 2000-2004 22·3 months) but not >60 years (12·7, 11·6 months).

INTERPRETATION

Population-level improvements in OS for dnMBC have not been consistently observed in rMBC cohorts nor older women. These findings have implications for counselling patients about prognosis, planning cancer services and trial stratification.

FUNDING

SL was funded in part by a National Health and Medical Research Council (NHMRC) Project Grant ID: 1125433. NH was funded by the NBCF Chair in Breast Cancer Prevention grant (EC-21-001) and a NHMRC Investigator (Leader) grant (194410). BD and SAP were funded in part by the NHMRC Centre of Research Excellence in Medicines Intelligence (1196900).

The validity of progression-free survival 2 as a surrogate trial end point for overall survival

BACKGROUND

Overall survival (OS) is the gold-standard end point for oncology trials. However, the availability of multiple therapeutic options after progression and crossover to receive investigational agents confound and delay OS data maturation. Progression-free survival 2 (PFS-2), defined as the time from randomization to progression on first subsequent therapy, has been proposed as a surrogate for OS. Using a meta-analytic approach, the authors aimed to assess the association between OS and PFS-2 and compare this with progression-free survival 1 (PFS-1) and the objective response rate (ORR).

METHODS

An electronic literature search was performed to identify randomized trials of systemic therapies in advanced solid tumors that reported PFS-2 as a prespecified end point. Correlations between OS and PFS-2, OS and PFS-1, and OS and ORR as hazard ratios (HRs) or odds ratios (ORs) were assessed via linear regression weighted by trial size.

RESULTS

Thirty-eight trials were included, and they comprised 19,031 patients across 8 tumor types. PFS-2 displayed a moderate correlation with OS (r = 0.67; 95% confidence interval [CI], 0.08-0.69). Conversely, correlations of ORR (r = 0.12; 95% CI, 0.00-0.13) and PFS-1 (r = 0.21; 95% CI, 0.00-0.33) were poor. The findings for PFS-2 were consistent for subgroup analyses by treatment type (immunotherapy vs nonimmunotherapy: r = 0.67 vs 0.67), survival post progression (<12 vs ≥12 months: r = 0.86 vs 0.79), and percentage not receiving subsequent treatment (<50% vs ≥50%: r = 0.70 vs 0.63).

CONCLUSIONS

Across diverse tumors and therapies, the treatment effect on PFS-2 correlated moderately with the treatment effect on OS. PFS-2 performed consistently better than PFS-1 and ORR, regardless of postprogression treatment and postprogression survival. PFS-2 should be included as a key trial end point in future randomized trials of solid tumors.

Impact of ultrasound on inguinal hernia repair rates in Australia: a population-based analysis

BACKGROUND

Inguinal hernias are a common pathology that often requires surgical management. The use of groin ultrasound (GU) to investigate inguinal hernias is a growing area of concern as an inefficient use of healthcare resources. Our aim was to assess changes in the rates of GU and the impact on surgical practice.

METHODS

Medicare Item Reports and the Australian Institute of Health and Welfare Database were used to estimate annual GU and inguinal hernia repair (IHR) rates per 100 000 population for the period 2000/2001-2017/2018. Pearson's correlation coefficients and linear regression analyses were performed to assess associations between these variables.

RESULTS

Over the 18-year period, GU rates increased 13-fold from 88 to 1174 per 100 000 population. Overall, total IHR rates decreased from 217 to 192 per 100 000. Overall, unilateral IHR rates have decreased (182-146 per 100 000), bilateral IHRs have increased (35-46 per 100 000), laparoscopic IHR has increased (30-86 per 100 000) and open surgery has declined (187-106 per 100 000). The increase in GU rates were strongly associated with the decrease in unilateral (r = -0.936, P = <0.001) and increase in bilateral IHR rates (r = 0.924, P = <0.001).

CONCLUSION

The use of GU has increased substantially, potentially representing an unnecessary cost to the healthcare system. Rising GU rates are not associated with an increase in IHR, however, may contribute to the increasing rates of bilateral IHRs. This study supports the opinion that more extensive clinical and health policy initiatives are needed in Australia to address this health issue.

Abstract P2-12-01: Real-world use and outcomes of trastuzumab for HER2+ metastatic breast cancer in Australia: Analysis of the herceptin program, 2001-2015

Aims

Between December 2001 and July 2015 Australian women with HER2-positive metastatic breast cancer (MBC) accessed trastuzumab in combination with taxane chemotherapy or as monotherapy via the government funded Herceptin Program (HP); we characterise their treatment patterns and survival outcomes.

Methods

This retrospective, whole-of-population cohort study used linked dispensing, medical services, and death records. We stratified patients into three year-of-trastuzumab-initiation groups: 1. 2001-2002 (may include patients accessing trastuzumab in later lines); 2. 2003 - October 2006 (likely first-line treated but prior to trastuzumab availability for early breast cancer (EBC)); and 3: October 2006–June 30 2015 (most representative of contemporary practice). Patients were observed until death or censored at June 30 2016.

We estimated duration of trastuzumab therapy from the initial dispensing date for MBC until 30 days after the last dispensing. We considered a gap of ≥90 days between trastuzumab dispensings a separate course of treatment. We estimated overall survival (OS) as the time from first trastuzumab dispensing until death from any cause. We used Kaplan-Meier methods to estimate the total duration of trastuzumab therapy and OS. We used dispensing dates of cancer medicines to determine concomitant treatments and used claims for echocardiography and MUGA scans to determine the timing of cardiac monitoring.

Results

5,895 patients accessed trastuzumab for MBC. Median age at trastuzumab initiation was 57 years (IQR: 48 – 66). 800 patients (22%) from Group 3 also received trastuzumab for EBC. Treatment details and OS are tabulated:

 Overall (n = 5,895)Group 1 (n = 495)Group 2 (n = 1,709)Group 3 (n = 3,691)Median time on trastuzumab for MBC, first course, months (IQR)13.2 (5.7 – 26.6)9.2 (3.8 – 22.5)12.3 (5.4 – 23.3)14.0 (6.1 – 29.8)Median OS from first trastuzumab dispensing for MBC, months (IQR)30.3 (13.4 – 68.7)19.8 (8.9 – 38.8)27.5 (12.5 – 58.9)34.6 (15.1 – 82.8)Patients initiating trastuzumab, n (%):    monotherapy1,571 (27)226 (46)625 (37)720 (20)+ taxane3,150 (53)157 (32)800 (47)2,193 (59)+ hormonal therapy763 (13)47 (9)169 (10)561 (15)+ non-taxane chemotherapy376 (6)65 (13)115 (7)217 (6)Cardiac assessment:    at baseline (60 days prior to 30 days following trastuzumab initiation)3,721 (63%)189 (38%)831 (49%)2,701 (73%)during treatment3,324 (56%)150 (30%)778 (46%)2,396 (65%)

Conclusions

Our real-world estimates of OS for each patient group are both similar to and shorter than those from clinical trials published during similar time periods. Group 3 median OS is 6 months shorter than the control arm of the CLEOPATRA study (34.6 v 40.8 months) while median duration of first trastuzumab course was 4 months longer (14.0 v 10.4 months), suggesting patients continue trastuzumab beyond progression. In Group 3, 25% of patients died within 15 months of starting trastuzumab, 50% survived beyond 3 years and 25% survived beyond 7 years. These estimates will be useful for clinicians discussing expected survival time with patients in routine practice. Although the cardiotoxicity of trastuzumab is well recognised, baseline cardiac assessment was not universal, even in the most recent cohort.

Citation Format: Daniels B, Kiely BE, Lord SJ, Houssami N, Pearson S-A. Real-world use and outcomes of trastuzumab for HER2+ metastatic breast cancer in Australia: Analysis of the herceptin program, 2001-2015 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-12-01.

ICare-ACS (Improving Care Processes for Patients With Suspected Acute Coronary Syndrome): A Study of Cross-System Implementation of a National Clinical Pathway

BACKGROUND

Efforts to safely reduce length of stay for emergency department patients with symptoms suggestive of acute coronary syndrome (ACS) have had mixed success. Few system-wide efforts affecting multiple hospital emergency departments have ever been evaluated. We evaluated the effectiveness of a nationwide implementation of clinical pathways for potential ACS in disparate hospitals.

METHODS

This was a multicenter pragmatic stepped-wedge before-and-after trial in 7 New Zealand acute care hospitals with 31 332 patients investigated for suspected ACS with serial troponin measurements. The implementation was a clinical pathway for the assessment of patients with suspected ACS that included a clinical pathway document in paper or electronic format, structured risk stratification, specified time points for electrocardiographic and serial troponin testing within 3 hours of arrival, and directions for combining risk stratification and electrocardiographic and troponin testing in an accelerated diagnostic protocol. Implementation was monitored for >4 months and compared with usual care over the preceding 6 months. The main outcome measure was the odds of discharge within 6 hours of presentation RESULTS: There were 11 529 participants in the preimplementation phase (range, 284-3465) and 19 803 in the postimplementation phase (range, 395-5039). Overall, the mean 6-hour discharge rate increased from 8.3% (range, 2.7%-37.7%) to 18.4% (6.8%-43.8%). The odds of being discharged within 6 hours increased after clinical pathway implementation. The odds ratio was 2.4 (95% confidence interval, 2.3-2.6). In patients without ACS, the median length of hospital stays decreased by 2.9 hours (95% confidence interval, 2.4-3.4). For patients discharged within 6 hours, there was no change in 30-day major adverse cardiac event rates (0.52% versus 0.44%; P=0.96). In these patients, no adverse event occurred when clinical pathways were correctly followed.

CONCLUSIONS

Implementation of clinical pathways for suspected ACS reduced the length of stay and increased the proportions of patients safely discharged within 6 hours.

CLINICAL TRIAL REGISTRATION

URL: https://www.anzctr.org.au/ (Australian and New Zealand Clinical Trials Registry). Unique identifier: ACTRN12617000381381.

The Osseointegration Group of Australia Accelerated Protocol (OGAAP-1) for two-stage osseointegrated reconstruction of amputated limbs

AIMS

This study describes the Osseointegration Group of Australia's Accelerated Protocol two-stage strategy (OGAAP-1) for the osseointegrated reconstruction of amputated limbs.

PATIENTS AND METHODS

We report clinical outcomes in 50 unilateral trans-femoral amputees with a mean age of 49.4 years (24 to 73), with a minimum one-year follow-up. Outcome measures included the Questionnaire for persons with a Trans-Femoral Amputation, the health assessment questionnaire Short-Form-36 Health Survey, the Amputation Mobility Predictor scores presented as K-levels, 6 Minute Walk Test and timed up and go tests. Adverse events included soft-tissue problems, infection, fractures and failure of the implant.

RESULTS

Our results demonstrated statistically significant improvements in all five outcome measures. A total of 27 patients experienced adverse events but at the conclusion of the study, all 50 were walking on osseointegrated prostheses.

CONCLUSION

These results demonstrate that osseointegrated prostheses are a suitable alternative to socket-fit devices for amputees experiencing socket-related discomfort and that our strategy offers more rapid progress to walking than other similar protocols. Cite this article: Bone Joint J 2016;98-B:952-60.

MIC-1/GDF15 in Barrett's oesophagus and oesophageal adenocarcinoma

Background:

Biomarkers are needed to improve current diagnosis and surveillance strategies for patients with Barrett's oesophagus (BO) and oesophageal adenocarcinoma (OAC). Macrophage inhibitory cytokine 1/growth differentiation factor 15 (MIC-1/GDF15) tissue and plasma levels have been shown to predict disease progression in other cancer types and was therefore evaluated in BO/OAC.

Methods:

One hundred thirty-eight patients were studied: 45 normal oesophagus (NE), 37 BO, 16 BO with low-grade dysplasia (LGD) and 40 OAC.

Results:

Median tissue expression of MIC-1/GDF15 mRNA was ⩾25-fold higher in BO and LGD compared to NE (P<0.001); two-fold higher in OAC vs BO (P=0.039); and 47-fold higher in OAC vs NE (P<0.001). Relative MIC-1/GDF15 tissue expression >720 discriminated between the presence of either OAC or LGD vs NE with 94% sensitivity and 71% specificity (ROC AUC 0.86, 95% CI 0.73–0.96; P<0.001). Macrophage inhibitory cytokine 1/growth differentiation factor 15 plasma values were also elevated in patients with OAC vs NE (P<0.001) or BO (P=0.015).

High MIC-1/GDF15 plasma levels (⩾1140 pg ml⁻¹) were an independent predictor of poor survival for patients with OAC (HR 3.87, 95% CI 1.01–14.75; P=0.047).

Conclusions:

Plasma and tissue levels of MIC-1/GDF15 are significantly elevated in patients with BO, LGD and OAC. Plasma MIC-1/GDF15 may have value in diagnosis and monitoring of Barrett's disease.

A prognostic nomogram to predict overall survival in patients with platinum-sensitive recurrent ovarian cancer

BACKGROUND

Patients with platinum-sensitive recurrent ovarian cancer have variable prognosis and survival. We extend previous work on prediction of progression-free survival by developing a nomogram to predict overall survival (OS) in these patients treated with platinum-based chemotherapy.

PATIENTS AND METHODS

The nomogram was developed using data from the CAELYX in Platinum-Sensitive Ovarian Patients (CALYPSO) trial. Multivariate proportional hazards models were generated based on pre-treatment characteristics to develop a nomogram that classifies patient prognosis based on OS outcome. We also developed two simpler models with fewer variables and conducted model validations in independent datasets from AGO-OVAR Study 2.5 and ICON 4. We compare the performance of the nomogram with the simpler models by examining the differences in the C-statistics and net reclassification index (NRI).

RESULTS

The nomogram included six significant predictors: interval from last platinum chemotherapy, performance status, size of the largest tumour, CA-125, haemoglobin and the number of organ sites of metastasis (C-statistic 0.67; 95% confidence interval 0.65-0.69). Among the CALPYSO patients, the median OS for good, intermediate and poor prognosis groups was 56.2, 31.0 and 20.8 months, respectively. When CA-125 was not included in the model, the C-statistics were 0.65 (CALYPSO) and 0.64 (AGO-OVAR 2.5). A simpler model (interval from last platinum chemotherapy, performance status and CA-125) produced a significant decrease of the C-statistic (0.63) and NRI (26.4%, P < 0.0001).

CONCLUSIONS

This nomogram with six pre-treatment characteristics improves OS prediction in patients with platinum-sensitive ovarian cancer and is superior to models with fewer prognostic factors or platinum chemotherapy free interval alone. With independent validation, this nomogram could potentially be useful for improved stratification of patients in clinical trials and also for counselling patients.

Effectiveness and cost-effectiveness of sentinel lymph node biopsy compared with axillary node dissection in patients with early-stage breast cancer: a decision model analysis

Background:

Sentinel lymph node biopsy (SLNB) is less invasive than axillary lymph node dissection (ALND) for staging early breast cancer, and has a lower risk of arm lymphoedema and similar rates of locoregional recurrence up to 8 years. This study estimates the longer-term effectiveness and cost-effectiveness of SLNB.

Methods:

A Markov decision model was developed to estimate the incremental quality-adjusted life years (QALYs) and costs of an SLNB-based staging and management strategy compared with ALND over 20 years’ follow-up. The probability and quality-of-life weighting (utility) of outcomes were estimated from published data and population statistics. Costs were estimated from the perspective of the Australian health care system. The model was used to identify key factors affecting treatment decisions.

Results:

The SLNB was more effective and less costly than the ALND over 20 years, with 8 QALYs gained and $883 000 saved per 1000 patients. The SLNB was less effective when: SLNB false negative (FN) rate >13% 5-year incidence of axillary recurrence after an SLNB FN>19% risk of an SLNB-positive result >48% lymphoedema prevalence after ALND <14% or lymphoedema utility decrement <0.012.

Conclusion:

The long-term advantage of SLNB over ALND was modest and sensitive to variations in key assumptions, indicating a need for reliable information on lymphoedema incidence and disutility following SLNB. In addition to awaiting longer-term trial data, risk models to better identify patients at high risk of axillary metastasis will be valuable to inform decision-making.

A systematic review of the effectiveness of magnetic resonance imaging (MRI) as an addition to mammography and ultrasound in screening young women at high risk of breast cancer

Breast magnetic resonance imaging (MRI) has been proposed as an additional screening test for young women at high risk of breast cancer in whom mammography alone has poor sensitivity. We conducted a systematic review to assess the effectiveness of adding MRI to mammography with or without breast ultrasound and clinical breast examination (CBE) in screening this population. We found consistent evidence in 5 studies that adding MRI provides a highly sensitive screening strategy (sensitivity range: 93-100%) compared to mammography alone (25-59%) or mammography plus ultrasound+/-CBE (49-67%). Meta-analysis of the three studies that compared MRI plus mammography versus mammography alone showed the sensitivity of MRI plus mammography as 94% (95%CI 86-98%) and the incremental sensitivity of MRI as 58% (95%CI 47-70%). Incremental sensitivity of MRI was lower when added to mammography plus ultrasound (44%, 95%CI 27-61%) or to the combination of mammography, ultrasound plus CBE (31-33%). Estimates of screening specificity with MRI were less consistent but suggested a 3-5-fold higher risk of patient recall for investigation of false positive results. No studies assessed as to whether adding MRI reduces patient mortality, interval or advanced breast cancer rates, and we did not find strong evidence that MRI leads to the detection of earlier stage disease. Conclusions about the effectiveness of MRI therefore depend on assumptions about the benefits of early detection from trials of mammographic screening in older average risk populations. The extent to which high risk younger women receive the same benefits from early detection and treatment of MRI-detected cancers has not yet been established.

Diabetes induces rapid suppression of adaptive immunity followed by homeostatic T-cell proliferation

Surprisingly, the effect of acute diabetes on immunity has not been examined in detail. We, herein, show for the first time that untreated acute diabetes causes rapid lymphopenia followed by homeostatic T-cell proliferation. The diabetes-induced lymphopenia was associated with an immunosuppressed state that could be sufficiently strong to allow engraftment of fully allogeneic beta-cells or block rejection of islet transplants. In contrast, homeostatic proliferation and recovery of T-cell numbers were associated with islet rejection. Thus, the timing of islet transplant challenge in relation to diabetes induction was critical in determining whether islets were accepted or rejected. In addition, we tested whether diabetes-related immunosuppression could result in an overestimation of the efficacy of a tolerance-inducing protocol. Consistent with this possibility, a protocol targeting CD40L and ICOS that we have shown induces tolerance in diabetic recipients was unable to induce tolerance in non-diabetic recipients. The data uncover a previously unrecognized suppressive effect of diabetes on adaptive immunity. Furthermore, they suggest that the standard methods of testing new tolerance-inducing protocols in islet transplantation require modification and that diabetes itself can contribute to homeostatic proliferation, a process associated with autoimmunity and a resistance to tolerance induction.

Reproductive factors and subtypes of breast cancer defined by hormone receptor and histology

Reproductive factors are associated with reduced risk of breast cancer, but less is known about whether there is differential protection against subtypes of breast cancer. Assuming reproductive factors act through hormonal mechanisms they should protect predominantly against cancers expressing oestrogen (ER) and progesterone (PR) receptors. We examined the effect of reproductive factors on subgroups of tumours defined by hormone receptor status as well as histology using data from the NIHCD Women's Contraceptive and Reproductive Experiences (CARE) Study, a multicenter case–control study of breast cancer. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) as measures of relative risk using multivariate unconditional logistic regression methods. Multiparity and early age at first birth were associated with reduced relative risk of ER + PR + tumours (P for trend=0.0001 and 0.01, respectively), but not of ER − PR − tumours (P for trend=0.27 and 0.85), whereas duration of breastfeeding was associated with lower relative risk of both receptor-positive (P for trend=0.0002) and receptor-negative tumours (P=0.0004). Our results were consistent across subgroups of women based on age and ethnicity. We found few significant differences by histologic subtype, although the strongest protective effect of multiparity was seen for mixed ductolobular tumours. Our results indicate that parity and age at first birth are associated with reduced risk of receptor-positive tumours only, while lactation is associated with reduced risk of both receptor-positive and -negative tumours. This suggests that parity and lactation act through different mechanisms. This study also suggests that reproductive factors have similar protective effects on breast tumours of lobular and ductal origin.