Influence of tumor cell proliferation and sex-hormone receptors on effectiveness of radiation therapy for dogs with incompletely resected meningiomas

Objective-To assess the influence of tumor cell proliferation and sex-hormo ne receptors on the efficacy of megavoltage irradiation for dogs with incom pletely resected meningiomas. Design-Longitudinal clinical trial. Animals-20 dogs with incompletely resected intra cranial meningiomas. Procedure-Dogs were treated with 48 Gy of radiation administered 3 times pe r week on an alternate-day schedule of 4 Gy/fraction for 4 weeks, using bil ateral parallel-opposed fields. Results-Tumor proliferative fraction measured by immunohistochemical detect ion of proliferating eel nuclear antigen (PFPCNA index) ranged from 10 to 4 2% (median, 24%). Progesterone receptor immunoreactivity was detected in 70 % of tumors. Estroger receptor immunoreactivity was not detected. Ar invers e correlation was found between detection of progesterone receptors and the PFPCNA index. The overall 2-year progression-free survival (PFS) rate was 68%. The only prognostic factor that significantly affected PFS rate was th e PFPCNA index. The 2-year PFS was 42% for tumors with a high PFPCNA index (value greater than or equal to 24%) and 91% for tumors with a low PFPCNA. index (value < 24%). Tumors with a high PFPCNA index were 9.1 limes as like ly to recur as were tumors with a low PFPCNA index. Conclusions and Clinical Relevance-This study confirms the value of irradia tion for dogs with incompletely resected meningiomas. Prognostic value of t he PFPCNA index suggests that duration of treatment and interval from surge ry to start of irradiation mat affect outcome. Loss of progesterone recepto rs in some tumors may be responsible for an increase in PFPCNA index and ma y indirectly affect prognosis after radiation therapy.