Spatial transcriptomic analysis of tumour with high and low CAIX expression in TNBC tissue samples using GeoMx™ RNA assay.

PURPOSE: Prognostic significance and gene signatures associated with carbonic anhydrase IX (CAIX) was investigated in triple negative breast cancer (TNBC) patients.

METHODS: Immunohistochemistry (IHC) for CAIX was performed in tissue microarrays (TMAs) of 136 TNBC patients.In a subset of 52 patients Digital Spatial Profiler (DSP) was performed in tumour (pan-cytokeratin+) and stroma (pan-cytokeratin-). Differentially expressed genes (DEGs) with P<0.05 and fold change ≥1 or ≤-1 were identified. Four genes were validated at the protein level.

RESULT: Cytoplasmic CAIX expression was independently associated with poor recurrence free survival in TNBC patients [hazard ratio (HR)=6.59, 95% confidence interval (CI): 1.47-29.58, P=0.014]. DEG analysis identified 4 up-regulated genes (CD68, HIF1A, pan-melanocyte, and VSIR) in the tumour region and 9 down-regulated genes in the stromal region (CD86, CD3E, MS4A1, BCL2, CCL5, NKG7, PTPRC, CD27, and FAS) when low versus high CAIX expression was explored. Employing IHC, high CD68 and HIF-1α was associated with poorer prognosis and high BCL2 and CD3 was associated with good prognosis.

CONCLUSIONS: DSP technology identified DEGs in TNBC. Selected genes validated by IHC showed involvement of CD3 and BCL2 expression within stroma and HIF-1α, and CD68 expression within tumour. However, further functional analysis is warranted.