SAN FRANCISCOPhotodynamic therapy (PDT), using light tuned to specific wavelengths in order to activate a previously administered photosensitizing drug, holds significant promise as a new treatment modality for malignancies of the oral cavity and larynx, said Vanessa Schweitzer, MD, clinical professor of otolaryngology at the University of Michigan and senior staff physician at Henry Ford Health Care Systems, Detroit. [See page 64 for more on new uses of PDT.]
Photodynamic therapy offers minimal postoperative side effects, produces no systemic toxicity, preserves voice quality and oral function, and is less expensive than conventional therapies, Dr. Schweitzer said.
In addition, she noted, clinical results suggest that multiple courses of treatment do not induce resistance. Drug-plus-light retreatments are both possible and beneficial given accurate diagnostic staging and tumor mapping.
Will It Replace Radiation Therapy?
By the end of the decade, Dr. Schweitzer told the 101st Annual Meeting of the American Academy of Otolar-yngology-Head and Neck Surgery, photodynamic therapy may have replaced radiation therapy for superficial oral cavity and a variety of laryngeal carcinomas.
The voice quality of patients is not hindered at all by this treatment, she noted, contrasting PDT with surgical and other therapeutic possibilities. Twenty-six centers across the United States, as well as centers in Canada and Europe, currently administer PDT, she added.
Retrospective studies of patients who have undergone photodynamic therapy for several different types of cancers at Henry Ford between 1983 and 1997 show extremely encouraging results, Dr. Schweitzer said. Phase II clinical trials of PDT have been conducted at Henry Ford for the past 10 years, she added.
Results of Retrospective Studies
Of 81 patients treated with the photosensitizer drug Photofrin (porfimer sodium) and subsequently exposed to light photoactivation, 75 showed complete or partial remission of their cancer. These patients included 39 with head and neck cancer; most of the others had esophageal cancer, Kaposis sarcoma, or large basal cell or squamous cell skin cancers.
Sixty of the patients responded after a single photodynamic treatment and 14 after two treatments. Only seven patients required three or four treatments. One course of photodynamic therapy for treatment of laryngeal cancer, Dr. Schweitzer said, costs less than a single six-week course of radiation therapy.
Of the 39 head and neck cancer patients, 12 had superficial diffuse field cancerization of the oral cavity or Tis; T1,N0,M0; and T2,N0,M0 laryngeal malignancies (squamous cell carcinoma and angiosarcoma) while the remaining 27 had stage III or IV disease.
All were cancers that had previously failed to respond to conventional treatment, including wide local surgical excision, CO2 laser ablation, or external beam radiation therapy. Of the 12 patients with early stage oral cavity and laryngeal cancers, 83% had a complete response, while all the remaining patients had a partial response. Results are less promising in patients with advanced disease, but still better than conventional therapies.
There is no systemic toxicity from this treatment whatsoever, Dr. Schweitzer noted. Nor does photodynamic treatment produce the kind of physical disfigurement that often results from surgical excision or directed beam radiation treatment. Patients themselves, as well as outside listeners, find no degradation of voice strength or quality after treatment.
The entire treatment is routinely conducted on an outpatient basis, which helps control costs. Photofrin is administered to patients by IV infusion at a rate of 2 mg/kg. Infusion is followed 48 to 60 hours later by intraoperative photoacti-vation from an argon pumped tunable dye laser at 630 nm via a microsurface lens fiberoptic or a cylindrical diffuser fiberoptic.
The surgical light dose depends on the size, shape, and location of the target tissue, she said. The photoactivating light dose for head and neck cancers is 50 to 100 j/cm2 at m/W/cm2.