Trastuzumab deruxtecan versus trastuzumab emtansine in HER2-positive metastatic breast cancer: long-term survival analysis of the DESTINY-Breast03 trial.

Trastuzumab deruxtecan (T-DXd) demonstrated significantly improved efficacy over trastuzumab emtansine (T-DM1) in DESTINY-Breast03 (median follow-up, 28 months). We report updated efficacy and safety analyses, including secondary and exploratory efficacy endpoints (median follow-up, 41 months) of DESTINY-Breast03. Patients with advanced HER2-positive metastatic breast cancer previously treated with taxane and trastuzumab were randomized to T-DXd (5.4 mg per kg (261 patients)) or T-DM1 (3.6 mg per kg (263 patients)). The primary endpoint was progression-free survival (PFS) by blinded independent central review and was previously reported. The key secondary endpoint was overall survival (OS). Other secondary endpoints included objective response rate, duration of response and PFS (all by investigator assessment) and safety. At data cutoff, 20 November 2023, median PFS by investigator assessment was 29.0 versus 7.2 months (hazard ratio (HR), 0.30; 95% confidence interval (CI), 0.24-0.38), the 36-month PFS rate was 45.7% versus 12.4% and median OS was 52.6 versus 42.7 months (HR, 0.73; 95% CI, 0.56-0.94) with T-DXd versus T-DM1, respectively. Treatment-emergent adverse events were consistent with the previous analyses. No new instances of grade ≥3 interstitial lung disease or pneumonitis occurred (all grade rate, 16.7% (T-DXd) versus 3.4% (T-DM1)). With longer follow-up, T-DXd continued to demonstrate superior efficacy over T-DM1 with a manageable safety profile. ClinicalTrials.gov registration: NCT03529110 .

How to identify patients with increased risk of breast cancer relapse?

A cohort of 362 breast cancer patients had subtype classification accomplished using 4 immunohistochemical markers: luminal A (ER or PR positive, HER2 negative, Ki-67<14%), luminal B (ER or PR positive, HER2 negative, Ki-67≥14%), luminal HER2 (ER or PR positive, HER2 positive), HER2 enriched (ER or PR negative, HER2 positive) or triple negative (ER, PR, and HER2 negative). Multivariable Cox analysis was used to determine the risk of local (LR) or distant (DR) relapse associated with the intrinsic subtypes, adjusting for standard clinicopathologic factors. There have been a total of 124 recurrences. Triple-negative patients were associated with increased risk of LR. Luminal B subtype showed statistical tendency (P=0.053) to LR. For patients undergoing breast conservation surgery, luminal B and HER2-enriched subtypes demonstrated an increased risk to LR, and this was statistically significant on multivariable analysis. After mastectomy, there was no statistical difference between subtypes of LR or DR on multivariable analysis. Luminal A tumors are associated with a low risk of LR or DR. Despite the existence of gene expression profiling, in the current study we demonstrate that analysis of 4 immunohistochemical markers is equally effective and less expensive alternative to identify higher recurrence risk patients.

Final overall survival: fulvestrant 500 mg vs 250 mg in the randomized CONFIRM trial.

BACKGROUND: At the time of the initial analysis of overall survival (OS) for the Comparison of Faslodex in Recurrent or Metastatic Breast Cancer (CONFIRM) randomized, double-blind, phase III trial, approximately 50% of patients had died. A final analysis of OS was subsequently planned for when 75% of patients had died. METHODS: Patients were randomly assigned 1:1 to fulvestrant 500 mg administered as two 5-mL intramuscular injections on days 0, 14, and 28 and every 28 (±3) days thereafter or fulvestrant 250 mg administered as two 5-mL intramuscular injections (one fulvestrant and one placebo [identical in appearance to study drug]) on days 0, 14 (two placebo injections only), and 28 and every 28 (±3) days thereafter. OS was analyzed using an unadjusted log-rank test. No adjustments were made for multiplicity. Serious adverse events (SAEs) and best response to subsequent therapy were also reported. All statistical tests were two-sided. RESULTS: In total, 736 women (median age = 61.0 years) were randomly assigned to fulvestrant 500 mg (n = 362) or 250 mg (n = 374). At the final survival analysis, 554 of 736 (75.3%) patients had died. Median OS was 26.4 months for fulvestrant 500 mg and 22.3 months for 250 mg (hazard ratio = 0.81; 95% confidence interval = 0.69-0.96; nominal P = .02). There were no clinically important differences in SAE profiles between the treatment groups; no clustering of SAEs could be detected in either treatment group. Type of first subsequent therapy and objective responses to first subsequent therapy were well balanced between the two treatment groups. CONCLUSIONS: In patients with locally advanced or metastatic estrogen receptor-positive breast cancer, fulvestrant 500 mg is associated with a 19% reduction in risk of death and a 4.1-month difference in median OS compared with fulvestrant 250 mg. Fulvestrant 500 mg was well tolerated, and no new safety concerns were identified.

Comparing duration of response and duration of clinical benefit between fulvestrant treatment groups in the CONFIRM trial: application of new methodology.

Comparisons of duration of response (DoR) and duration of clinical benefit (DoCB) within clinical trials are prone to biases. To address these biases, we used new methodology to prospectively analyze expected DoR and expected DoCB. Objective response rate and clinical benefit rate were calculated for fulvestrant 500 and 250 mg, and used to calculate expected DoR and expected DoCB for each dose group. The ratios for expected DoR and expected DoCB (expected DoR500/expected DoR250 and expected DoCB500/expected DoCB250) were then calculated, thereby allowing statistical comparisons of these endpoints between each arm of the COmparisoN of Faslodex In Recurrent or Metastatic breast cancer (CONFIRM) trial. Expected DoRs for fulvestrant 500 and 250 mg were 3.2 and 3.6 months, respectively. The expected DoR ratio between fulvestrant 500 and 250 mg was not statistically significant (0.89; 95 % CI, 0.48-1.67, P = 0.724). The expected DoCBs for fulvestrant 500 and 250 mg were 9.8 and 7.2 months, respectively. The expected DoCB ratio showed that the expected DoCB for fulvestrant 500 mg was significantly improved compared with the expected DoCB for fulvestrant 250 mg (1.36; 95 % CI, 1.07-1.73, P = 0.013). Analysis of the expected DoR and expected DoCB showed fulvestrant 500 mg significantly increased expected DoCB compared with fulvestrant 250 mg in the CONFIRM trial.

Results of the CONFIRM phase III trial comparing fulvestrant 250 mg with fulvestrant 500 mg in postmenopausal women with estrogen receptor-positive advanced breast cancer.

PURPOSE: We compared fulvestrant 500 mg regimen with the approved dose of fulvestrant 250 mg per month for treatment of postmenopausal women with estrogen receptor-positive advanced breast cancer who experienced progression after prior endocrine therapy. PATIENTS AND METHODS: Comparison of Faslodex in Recurrent or Metastatic Breast Cancer (CONFIRM) is a double-blind, parallel-group, multicenter, phase III study. Patients were randomly assigned to fulvestrant 500 mg (500 mg intramuscularly [IM] on day 0, then 500 mg IM on days 14 and 28 and every 28 days thereafter) or 250 mg every 28 days. Primary end point was progression-free survival (PFS). Secondary end points included objective response rate, clinical benefit rate (CBR), duration of clinical benefit (DoCB), overall survival (OS), and quality of life (QOL). RESULTS: PFS was significantly longer for fulvestrant 500 mg (n = 362) than 250 mg (n = 374) (hazard ratio [HR] = 0.80; 95% CI, 0.68 to 0.94; P = .006), corresponding to a 20% reduction in risk of progression. Objective response rate was similar for fulvestrant 500 mg and 250 mg (9.1% v 10.2%, respectively). CBR was 45.6% for fulvestrant 500 mg and 39.6% for fulvestrant 250 mg. DoCB and OS were 16.6 and 25.1 months, respectively, for the 500-mg group, whereas DoCB and OS were 13.9 and 22.8 months, respectively, in the 250-mg group. Fulvestrant 500 mg was well tolerated with no dose-dependent adverse events. QOL was similar for both arms. CONCLUSION: Fulvestrant 500 mg was associated with a statistically significant increase in PFS and not associated with increased toxicity, corresponding to a clinically meaningful improvement in benefit versus risk compared with fulvestrant 250 mg.