Prediction of Tumor Shrinkage in Acromegaly

In the last two decades, somatostatin analogs have become a cornerstone of medical therapy for acromegaly. One year of treatment with octreotide-LAR (LAR) controls GH and IGF-I excess in 54% and 63% of unselected patients, with an increasing proportion of subjects achieving IGF-I normalization prolonging the treatment. Clinically significant tumor shrinkage (20-30% vs. baseline) has also been reported, with a higher proportion in patients treated first-line \[231 of 448 patients (52%)\] than in those treated after surgery and/or radiotherapy \[52 of 248 patients (21%)\]. The highest rate of clinically significant shrinkage (\>20%) occurred in patients treated first-line with LAR (80%) as compared to the short-lasting octreotide formulation (50%) or lanreotide slow-release formulation (35%. In 99 de novo patients with acromegaly, we recently reported control of GH levels in 57.6%, of IGF-I levels in 45.5% and a greater than 50% tumor shrinkage in 44.4% after 12 months of first-line treatment with somatostatin analogues, either LAR or lanreotide. Besides the different drug used, the duration of treatment also plays an important role on the shrinkage magnitude. In a homogeneous cohort of 56 patients treated with LAR only and continuously for 24 months, we noted an even more sustained effect on tumor shrinkage: overall, tumor volume decreased by 68.1±16.5% using dosages up-titrated to 40 mg every 28 days. Despite this evidence, there is still a debate on the use of first-line treatment with somatostatin analogues. Of paramount importance would be the possibility to predict the results of one year treatment early after treatment beginning. Controversy has been reported on the predictive value of initial tumor size, inhibition of GH and IGF-I levels during treatment, and dose or type of the somatostatin analogue used during treatment. We found that percent suppression of IGF-I after 12 months of LAR treatment was the parameter that best predicted the amount of tumor shri