Consistent with previous observations7–9,13, the MBCs with predominant chondroid metaplasia included in this study lacked mutations affecting PIK3CA and Ras pathway genes, whereas TP53 mutations were found to be less frequent in MBCs with predominant spindle cell component compared to squamous and chondroid MBCs. The gene discussed is PIK3CA; the disease is maternal uniparental disomy of chromosome 20.