Effect of pituitary‐dependent hypercortisolism on the survival of dogs treated with radiotherapy for pituitary macroadenomas

BACKGROUND: Radiotherapy (RT) is an effective treatment for dogs presented with neurologic signs caused by pituitary tumors. However, its impact on the outcome of concurrent pituitary‐dependent hypercortisolism (PDH) is controversial. OBJECTIVES: Determine whether dogs with PDH have longer survival after pituitary RT compared with dogs with nonhormonally active pituitary masses and to evaluate whether clinical, imaging, and RT variables affect survival. ANIMALS: Ninety‐four dogs divided into 2 groups: PDH and non‐PDH, based on the presence of hypercortisolism. Forty‐seven dogs were allocated to the PDH group and 47 to the non‐PDH group. METHODS: Retrospective cohort study in which clinical records of dogs undergoing RT for pituitary macroadenomas between 2008 and 2018 at 5 referral centers were retrospectively evaluated. RESULTS: Survival was not statistically different between PDH and non‐PDH groups (median survival time [MST], 590 days; 95% confidence interval [CI], 0‐830 days and 738 days; 95% CI, 373‐1103 days, respectively; P = .4). A definitive RT protocol was statistically associated with longer survival compared with a palliative protocol (MST 605 vs 262 days, P = .05). The only factor statistically associated with survival from multivariate Cox proportional hazard analysis was total radiation dose (Gy) delivered (P < .01). CONCLUSIONS AND CLINICAL IMPORTANCE: No statistical difference in survival was identified between the PDH and non‐PDH groups, and longer survival was associated with higher Gy delivered.