Abstract
BACKGROUND: Lynch syndrome is an autosomal dominant condition that leads to an increased risk of many neoplasms. In the United Kingdom, NICE recommends that patients with colorectal and endometrial cancer should be tested for Lynch syndrome. There is conflicting evidence in the literature on the link between breast cancer and Lynch syndrome. CASE PRESENTATION: A 54-year-old woman presented with a lump in her right breast with a background of locally advanced colorectal cancer and Lynch syndrome due to a MLH1 gene mutation. A core biopsy showed a grade 3, invasive, triple-negative NST carcinoma. The tumour was triple-negative with patchy positivity for CK14 and CK5/6. Simultaneously, a cystic skin lesion in the contralateral breast was noted, which comprised lesional cells with a proliferation of clear cells and bland basaloid cells. The lesion had evidence of sebaceous differentiation with AR, podoplanin and p63 positivity. MSH1 and PMS2 deficiency was found in the breast and skin lesions. CONCLUSIONS: In Lynch syndrome, it is vital to be aware of the increased risk of various types of cancer. This case adds to the body of evidence of the spectrum of malignancies that can be encountered in patients with Lynch syndrome.