DEFENDOR SPECIAL: Effect of primary prophylaxis with empegfilgrastim on pCR rate after neoadjuvant TCHP in early HER2+ breast cancer patients—Matching-adjusted indirect comparison (MAIC).

e13011 Background: TCHP (docetaxel, carboplatin, trastuzumab plus pertuzumab) is a preferred regimen for neoadjuvant therapy (NAT) of HER2-positive early breast cancer (HER2+ eBC) and requires primary G-CSF prophylaxis (PP). Various studies highlight the prognostic significance of pathological complete response (pCR, ypT0/is ypN0) for improving clinical outcomes. This analysis was designed to compare the pCR after NAT TCHP with PP by empegfilgrastim using DEFENDOR SPECIAL observational study data (NCT04905329) and cohort from KRISTINE study (NCT02131064) in which G-CSF were used for both primary and secondary febrile neutropenia (FN) prophylaxis in pts with HER2+ eBC at the investigator's discretion (i.e. real practice). Methods: We assessed the results of neoadjuvant TCHP in patients with HER2+ eBC and performed MAIC of pCR in patients who received empegfilgrastim in the DEFENDOR SPECIAL trial and in KRISTINE participants who received G-CSF in the same manner as in routine clinical practice . Individual patient data from DEFENDOR SPECIAL were weighted using confounding variables to match published patient characteristics of KRISTINE study. We accounted the following effect modifiers and prognostic factors: proportion of HER2+ pts by IHC2+FISH+; proportion of pts with IIIB-IIIC stages; proportion of pts with ER/PR negative status; proportion of pts with ECOG 1; median age (age); median time (in weeks) since diagnosis. We used logistic regression to estimate corresponding odds ratios (OR). Results: After weighting, patient characteristics were well balanced. The effective sample size was 17. Matching-adjusted indirect comparison showed statistically significant improvement of pCR (2.27 [95% CI: 1.12-4.93]) with empegfilgrastim vs real practice of G-CSF PP (Table 1). Conclusions: In conclusion, this analysis suggests that primary empegfilgrastim (long-acting G-CSF) prophylaxis has significant pCR benefit in contrast to a Kristine study cohort investigating physician choice of primary and secondary FN prophylaxis with various G-CSF in HER2+ eBC pts after TCHP. MAIC of pCR in HER2+ eBC pts after TCHP with empegfilgrastim vs. real world practice of G-CSF as PP of FN. Correction ESS OR 95% CI- 95%CI + pCR, ypT0/is ypN0 No 80 1,33 0,79 2,27 Yes 17 2,27 1,12 4,93 ESS- effective sample size.