Follow-up of pituitary tumor volume in patients with acromegaly treated with pegvisomant in clinical trials

Objective: We examined pituitary tumor volumes in patients treated with pegvisomant for 18 months or longer and in whom the tumors were monitored for at least 3 years. We present details on 9 of 304 patients in clinical trials with pegvisomant who experienced tumor growth within the first year of treatment. Method: Magnetic reonance images prior to start of pegvisomant and at last follow-up were examined in 43 patients (14% of participating patients). Twenty-nine had received prior radiation therapy (18% of irradiated patients and all but live received somatostatin analogs between periods of pegvisomant treatment. Results: At follow-up, the received tumor volume was 0.6 cc (range 0.0-19.7 ccl. in comparison with 1.6 cc (0.0-19.7 cc) at baseline (P<0.001). Twenty-five patients, of which 23 received radiation therapy, had tumor volume reduction therapy, had an increase in tumor volume from 1.61 to 1.93 cc. Of the nine patients with tumor growth, six had progressive growth before initiating pegvisomant. Two patients with stable tumors while on octreotide experienced enlargement after octreotide discontinuation but remained stable on long-term pegvisomant therapy. Conclusion: The present data indicate that pegvisomant does not promote tumor growth and suggest that the nine observed cases of tumor progression. which occured within 8 months after commencing pegvisomant, are likely rebound expansions after discontinuation of somatostatin analogs and/or the natural history of aggressively growing pituitary tumors. Continued long-term surveillance of tumor volume, particularly in non-irradiated patients is recommended.