EFFICACY OF PHOTODYNAMIC THERAPY ON ORIGINAL AND RECURRENT RAT MAMMARY-TUMORS

Photodynamic therapy has demonstrated efficacy toward primary, metasta tic and recurrent human tumors. Here, we investigated the ability of p hotodynamic therapy, using Photofrin(R), to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The resu lts demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photod ynamic therapy protocol, with mean tumor volume doubling times of simi lar to 11 days in both cases. Cells cultured from original tumor impla nts or tumors that recurred after photodynamic treatment accumulate eq uivalent amounts of [C-14]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals admini stered 5 mg/kg Photofrin(R) and exposed to light in vitro displayed co mparable phototoxicity. Additionally, examination of tumors by light m icroscopy revealed no morphological differences between the original t umor implants and the recurrent lesions. Taken together, these data in dicate that lesions which recurred at the site of the initial photodyn amic treatment were not resistant to a second identical course of phot odynamic therapy.