What question did this study set out to answer?

To investigate the impact of diagnostic delays on survival outcomes in rare cancers, specifically focusing on mTNBC.

March 12, 2026Open Access

293P Impact of diagnostic delay in rare cancers: Experiences and perspectives of patients and healthcare professionals

Key Points

To investigate the impact of diagnostic delays on survival outcomes in rare cancers, specifically focusing on mTNBC.
Analyzed alterations in PIK3CA, pTERT, and PTEN in mTNBC
Estimated tumor mutational burden and immune cell infiltration
Compared overall survival rates based on ERBB3 expression
Utilized insurance claims data for real-world overall survival analysis
ERBB3-High mTNBC showed significant mutations in TP53, providing improved overall survival.
Higher prevalence of PD-L1 expression associated with ERBB3-High tumors.
Proinflammatory immune cell fractions were elevated in ERBB3-High compared to ERBB3-Low samples.
Patients with ERBB3-High had a median overall survival of 31 months versus 20 months in ERBB3-Low cases.

Abstract

22C3; CPS >1%, SP142: IC >1%).High tumor mutational burden (TMB-H) was defined as >10 mut/MB.Cell infiltration in the tumor microenvironment was estimated by quanTIseq.Real world overall survival (OS) was inferred from insurance claims data and calculated from time of biopsy to last contact.Results: mTNBC more frequently harbored alterations in PIK3CA (45% vs 15%), pTERT (40% vs 3%) and PTEN (17% vs 8%), with higher prevalence of PD-L1 expression (22C3: 46% vs 35%; SP142: 59% vs 44%) (p<0.05).ERBB3-High mTNBC was more frequently associated with mutations in TP53 (86% vs 58%), RB1 (15% vs 2%), KMT2C (10% vs 1%) and TMB-H (12% vs 1%), while ERBB3-Low associated with mutations in PIK3CA (56% vs 33%) and pTERT (59% vs 17%) (p<0.05).Proinflammatory immune cell fractions were higher in ERBB3-High samples, while anti-inflammatory cell fractions were higher in ERBB3-Low.Interestingly, patients with ERBB3-High mTNBC had prolonged OS compared to those with ERBB3-Low (HR = 0.57, 95% CI (0.39 -0.83); median 31 vs. 20 months; p=0.0032). Conclusions:We observed an improvement in OS in patients with ERBB3-High mTNBC, suggesting that ERBB3 may represent a prognostic biomarker in this rare subtype.This work also highlights a potential treatment strategy for this chemo-refractory rare cancer and supports further investigation of HER3-targeting antibodies (such as Patritumab-deruxtecan) with or without checkpoint blockade for mTNBC.Validation in a larger cohort with corresponding clinicopathological data is in progress.

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