Immunohistochemistry-based taxonomical classification of bladder cancer predicts response to neoadjuvant chemotherapy
Platinum-based neoadjuvant chemotherapy (NAC) increases the survival of patients with organ-confined urothelial bladder cancer (UBC). Because not all patients benefit from treatment, NAC has not been widely applied in the clinical setting. There is strong evidence, based on retrospective studies, that patients with Basal/Squamous (BASQ)-like tumours present with more advanced disease and have worse prognosis; global transcriptomics can identify tumour subtypes associated with response to NAC. We aimed to investigate whether tumour immunohistochemical (IHC) subtyping predicts NAC response. Patients with muscle-invasive UBC having received platinum-based NAC were identified in two hospitals in Spain. Tissue microarrays were constructed; RNA and DNA were extracted from full sections. Nanostring analysis and immunohistochemistry to identify BASQ-like tumours and mutational analysis of UBC oncogenes. We used hierarchical clustering to classify 126 tumours and adjusted logistic regression to assess association with treatment response. Outcomes were progression-free survival and disease-specific survival; univariable and multivariate Cox regression models were applied. We found very high concordance between mRNA and protein for the 4 markers analyzed. We identified three main subgroups: BASQ-like (FOXA1/GATA3 low; KRT5/6/14 high), Luminal-like (FOXA1/GATA3 high; KRT5/6/14 low), and mixed-cluster (FOXA1/GATA3 high; KRT5/6 high; KRT14 low). Patients with BASQ-like tumours were more likely to achieve a pathological response to NAC, displaying a disease-specific survival similar to that of the remaining patients. In conclusion, patients with BASQ-like tumours - identified through simple and robust immunohistochemistry - have a higher likelihood of undergoing a pathological complete response to NAC. Prospective validation in independent series is required.\n\nNovelty and impactNeoadjuvant chemotherapy is an important component of the management of patietns with muscle-invasive bladder cancer but improved stratification is necessary. This retrospective study shows that patients with BASQ-like tumors can be identified using immunohistochemistry on paraffin-embedded tissue and are 4-fold more likely to achieve a pathological complete response to platinum-based NAC. The disease-specific survival of patients with BASQ-like tumours treated with NAC was not different from that of other tumour subtypes.