Quality aspects of the tissue microarray technique in a population‐based cohort with ductal carcinoma in situ of the breast

Aims: Tissue microarray (TMA) is an efficient technique for analysis of molecular markers. Prospectively collected samples have been reported to give excellent concordance between TMA data and corresponding whole‐sections. The aim was to evaluate the usefulness of TMA in a population‐based cohort of 213 women with ductal carcinoma in situ of the breast (DCIS). Methods and results: We studied immunohistochemical HER2, oestrogen (ER) and progesterone (PR) receptor status. The prognostic impact was similar for all markers comparing whole sections and TMAs. The proportion of positive tumours was similar regarding HER2 and ER, whereas PR tumours were more frequently positive in the TMAs (P = 0.007). The concordance was 80% (κ value 0.63) between original sections and TMAs. The proportion of successfully analysed tumours was 70%. Smaller tumours had a lower ratio (P < 0.0001) and a larger proportion of mismatched results (P = 0.05). Conclusions: Retrospective analyses of tumours from cohorts with long‐term follow‐up are indispensable. We have shown that the TMA technique is a useful tool for high‐throughput analysis of DCIS. However, our study has pinpointed some technical hazards within a population‐based cohort, including many small lesions and the poor condition of some donor blocks. Mismatched results may be due to tumour heterogeneity.