Late dermal effects of breast cancer radiotherapy

Abstract Radiotherapy is used in the treatment of breast cancer in order to reduce local recurrence rate. However, radiation is known to cause both acute and delayed side-effects on normal tissues. A common late complication of radiotherapy is fibrosis of skin and other organs. Fibrosis has been described as excessive accumulation of extracellular matrix components, especially collagens. Collagens are a group of extracellular matrix proteins that provide connective tissues with tensile strength. Type I and III collagens are the major structural proteins in skin. Alterations in collagen synthesis occur in various pathological conditions, during ageing and in association with diverse medical therapies. Collagens are degraded by matrix metalloproteinase enzymes (MMPs). The activity of MMPs is restrained by their specific tissue inhibitors (TIMPs). Elastic fibres constitute about 2–4% of skin dry weight. Despite their low quantity, elastic fibres are responsible for the resilient and elastic properties of skin. Dermal elastic fibres may be affected by intrinsic ageing, by extrinsic reasons such as photodamage and in several connective tissue diseases. The effect of radiotherapy on human skin type I and III collagen synthesis was investigated in a group of women who had been treated for breast cancer surgically and with radiotherapy. The levels of MMP-9, MMP-2/TIMP-2 complex, TIMP-1 and TIMP-2 in irradiated skin were also analysed. The effect of radiotherapy on elastic fibres was analysed using skin samples. The physio-mechanical properties of radiotherapy-treated skin were studied using ultrasound and elastometer devices, and compared with those of non-treated skin. In addition, skin samples were stained for haematoxylin-eosin, tenascin and mast cells. Factor VIII immunostaining was performed to visualize dermal blood vessels. Wound regeneration in irradiated skin was also studied using suction blister as a model. The synthesis of type I and III collagens was markedly increased as a result of radiotherapy. An increased amount of cross-linked type I collagen was detected in irradiated skin, and collagen turnover was also increased in irradiated skin. No difference in the amount or structure of the elastic fibres could be found between radiotherapy-treated and non-treated skin. A slight increase of skin thickness and stiffness was found in irradiated skin compared to non-treated skin. Increased tenascin expression was found in irradiated skin. The number of dermal blood vessels visualized by FVIII immunostaining was slightly higher in irradiated than in control skin. The amount of mast cells positive for tryptase, Kit receptor and chymase was increased in the upper dermis of irradiated skin. No difference in epidermal regeneration was found between irradiated and non-treated skin. The results of this study suggest that alteration of collagen metabolism contributes to dermal side effects of therapeutic irradiation