Fibroblast differentiation in subcutaneous fibrosis after postmastectomy radiotherapy

In order to acquire a better understanding of the mechanism of radiation-in duced fibrosis, we studied the differentiation of normal skin fibroblasts c ultured from breast cancer radiotherapy patients with different risk of fib rosis. The differentiation state of fibroblasts was characterized in clonal cultures using established cytomorphological criteria. Collagen synthesis was determined by H-3-proline incorporation into pepsin-resistant protein. Radiation-induced inactivation of fibroblasts was paralleled by an increase in terminally differentiated fibrocytes, demonstrating that premature term inal differentiation is an important response to irradiation of fibroblasts from radiotherapy patients. Surviving colony-forming fibroblasts showed a change in differentiation with an increase in the ratio L:E of progenitor f ibroblasts in late (L) compared to early (E) differentiation states. Furthe rmore, increased collagen production was observed after irradiation. The re sults provide evidence supporting a role of terminal fibroblast differentia tion in radiation-induced fibrosis and imply that the progenitor population surviving radiotherapy might be more prone to terminal differentiation tha n before radiotherapy.