Photodynamic therapy with aminolevulinic acid can be modified by pretreatment regimens with drugs such as 5- Fluorouracil (5-FU) or Vitamin D (calcitriol) that enhance accumulation of protoporphyrin IX (PpIX) within tumor tissue which presumably will enhance the therapeutic response to light. However, histological approaches for monitoring therapeutic responses are poorly suited for studying long term survival because large numbers of mice need to be sacrificed. To address this limitation, a non-invasive model to monitor tumor regression and regrowth has been established. Breast cancer cells, stably transfected with firefly luciferase (MDA-Luc cell line), are implanted orthotopically in nude mice (0.25 - 1 x 106 cells/site), and monitored 0-60 min after s.c. injection of luciferin, with Xenogen in-vivo imaging system. Luminescence is detectable at day 1 post-implantation. Tumors are suitable for experimentation on day 6, when daily injections of pretreatment agents (5-FU, 300 mg/kg; calcitriol, 1 μg/kg) begin. On day 9, ALA (75 mg/kg i.p.) is given for 4 hr, followed by illumination (633 nm, 100 J/cm2). Tumor luminescence post- PDT is monitored daily and compared with caliper measurements. Pretreatments (5-FU, calcitriol) by themselves do not inhibit luciferase expression, and all tumors grow at a similar rate during the pretreatment period. Results from in vivo survival experiments can be correlated to survival responses of MDA-Luc cells grown in monolayer cultures ± PDT and ± pretreatments, and additional mechanistic information (e.g. Ki67 and E-cadherin expression) obtained. In summary, this noninvasive model will permit testing of the therapeutic survival advantages of various pretreatments during cPDT.