Results of a phase 2 trial show that a high number (49%) of patients with advanced differentiated thyroid cancers responded to treatment with pazopanib, a drug that works by stopping tumour blood vessel growth. An estimated two-thirds of these patients are likely to have response lasting longer than 1 year. These findings published in The Lancet Oncology, show the highest response rate to date of any treatment for advanced thyroid cancer.

Over the past decade, the incidence of thyroid cancer has doubled. Fortunately, most patients with differentiated thyroid cancers have a favourable prognosis with the use of traditional treatments including surgery and radioiodine. However, 5% of these patients develop rapidly progressing life-threatening disease that has few treatment options. Recent research has shown that antiangiogenetic drugs (that target the growth of new blood vessels that allow tumours to grow and spread) have promising clinical activity in some patients with differentiated thyroid cancers.

In this study, Keith Bible from the Mayo Clinic, Rochester, USA, and international colleagues assessed the efficacy and safety of pazopanib, a drug that targets receptors on proteins involved in angiogenesis including vascular endothelial growth factor (VEGF), platelet-derived growth factor, and c-Kit.

Of the 37 patients with advanced, rapidly progressing thyroid cancer enrolled in the study, 18 (49%) had their tumours shrink (a partial response).

Interestingly, a higher number of patients with follicular thyroid cancer (73%) than with the more common papillary thyroid cancer (33%) had partial responses to treatment.

Side effects were frequent but generally mild. The most common were diarrhoea, hypertension, and raised aminotransferase concentrations. Treatment dose was lowered in 15 (41%) patients because of adverse events.

The authors conclude: "The partial response rate for pazopanib in our study seems very favourable in the light of results from previous trials and, to our knowledge, represents the highest response rate yet reported in patients with differentiated thyroid cancers. Moreover, pazopanib seemed to modify the disease course in responders."

In a Comment, Martin Schlumberger from the Institut Gustave Roussy in France says: "Additional trials are needed to compare the efficacy and toxic effects of kinase inhibitors, used alone or in combination with conventional treatments, and to determine the benefits in terms of progression-free and overall survival...Patients should preferably be included in such trials rather than be treated off-label with drugs that are available for other cancer types."

Source: Lancet Oncology, for abstract click here