Alterations in collagen fibre patterns in breast cancer. A premise for tumour invasiveness?

Stromal tissue in the breast plays a key role in cancer invasiveness due to molecular and cellular changes. Collagen is the main component of the stroma. The purposes of this study were to investigate differences in collagen fibre patterns between tumour-induced stromal tissue and normal stroma, and between high-grade and low-grade breast cancer stroma, using second harmonic generation microscopy. Thirty-seven ductal carcinomas were examined: Twenty-one Luminal A phenotype and sixteen HER2 or Basal-like phenotype. Three regions were examined in each case: intratumoral, juxtatumoral and extratumoral. Two images were captured in each region. Two characteristics of collagen fibres were examined: the degree of straightness, and the degree of alignment. Collagen fibres were visually classified as curly, intermediate or straight, and as parallel or not parallel. The results of angle measurement and visual analysis showed that collagen fibres were straightest in the intratumoral region and curliest in the extratumoral region. Collagen fibres were more parallel in the juxtatumoral region compared to the two other regions. There were no significant differences between high-grade and low-grade tumours. As a breast tumour progresses, collagen fibres appear to straighten and align at the tumour boundary. This could facilitate invasion of the tumour into the surrounding stroma.