Droplet-digital PCR reveals frequent mutations in TERT promoter region in breast fibroadenomas and phyllodes tumours, irrespective of the presence of MED12 mutations

Background Breast fibroadenoma (FA) and phyllodes tumour (PT) often have variations of gene mediator complex subunit 12 ( MED12 ) and mutations in the telomerase reverse transcriptase promoter region ( TERTp ). TERTp mutation is usually tested by Sanger sequencing. In this study, we compared Sanger sequencing and droplet-digital PCR (ddPCR) to measure TERTp mutations in FA and PT samples. Methods FA and PT samples were collected from 82 patients who underwent surgery at our institution from 2005 to 2016. MED12 mutations for all cases and TERTp mutations for 17 tumours were detected by Sanger sequencing. ddPCR was performed to analyse TERTp mutation in all cases. Results A total of 75 samples were eligible for analysis. Sanger sequencing detected MED12 mutations in 19/44 FA (42%) and 21/31 PT (68%). Among 17 Sanger sequencing-tested samples, 2/17 (12%) were TERTp mutation-positive. In ddPCR analyses, a significantly greater percentage of PT (19/31, 61%) was TERTp mutation-positive than was FA (13/44, 30%; P = 0.0046). The mutation positivity of TERTp and MED12 did not correlate, in either FA or PT. Conclusions ddPCR was more sensitive for detecting TERTp mutation than Sanger sequencing, being able to elucidate tumorigenesis in FA and PT.