Adenoid cystic carcinoma (ACC) of the breast is a rare tumour. Its recognition as a special type of breast carcinoma is very important because its prognosis is better than the not-otherwise-specified invasive ductal carcinoma and its treatment may not include axillary dissection. Tubular adenosis (TA) is a very rare condition of the breast that is histologically benign; however, it has been described in association with invasive ductal carcinoma. There are scant data regarding the molecular genomic alterations in ACC of the breast and no data has been presented on TA. Herein, we provide a morphological characterisation of TA arising synchronically with ACC in the breast. To characterise these lesions, we performed ultrastructural analysis, three-dimensional reconstruction and molecular analysis using immunohistochemistry and comparative genomic hybridisation. The copy number alterations found in ACC were restricted to small deletions on 16p and 17q only, whereas the TA harboured gains on 1q, 5p, 8q, 10q, 11p and 11q and losses on 1p, 10q, 11q, 12q, 14q, 15q and 16q. These molecular data highlight the genomic instability of TA, a benign florid proliferation intermingled with ACC, and do not provide evidence of molecular evolution from TA to ACC.