The aim of the study was to compare the structural changes in ultrasound image of the thyroid tissue in 12 women with breast cancer (BC) and 8 women with colorectal cancer (CC). MATLAB software was used to analyse the digitised images. As quantitative descriptors of thyroid ultrasound images (QDTI) were used raw grey scale values of individual image pixels (RAW) and the optimal one-dimensional discriminative texture features (F2, F6, F7). The possible relations between QDTI and thyroid laboratory parameters were tested. In the BC group serum levels of antibodies to thyroid peroxidase negatively correlated with feature RAW (multiple regression, beta coefficient -0.75, p=0.004) and positively with feature F2 (multiple regression, beta coefficient 1.44, p=0.04). In the BC group RAW negatively correlated with serum levels of tumour marker CA 15-3 (Pearson's correlation coefficient, r=-0.714, p=0.00917). No such correlations were found in CC group. The correlations between QDTI and serum levels of antibodies to thyroid peroxidase in patients with BC show that the positivity of antibodies to thyroid peroxidase is probably accompanied with structural changes in the thyroid tissue.