The cost impact of this guidance will depend on: the number of patients with unresectable and/or metastatic GIST; the proportion of patients who receive imatinib; the proportion of patients who respond to imatinib treatment; the duration of treatment; the price of imatinib; and the number of patients already prescribed imatinib for GIST.
Estimates of the annual incidence of GIST vary considerably. The manufacturer of imatinib estimated the number of new cases of unresectable and/or metastatic GIST to be between 80 and 240 people each year. It has also been suggested that current estimates of the incidence of GIST are underestimates, and these figures may increase as more tumours of patients with GIST are tested for c-KIT. The annual drug cost of imatinib is just under £19,000. Assuming that there will be 240 new patients eligible for imatinib treatment for GIST and that patients will be monitored by an average of 4 CT scans per year, the total cost of treating new patients in accordance with the guidance will be approximately £4.7 million in the first year. Assuming that the incidence rate does not change and that patients remain on imatinib treatment for an average of 1.44 years (as predicted by the DSU economic model), the total cost of treating patients with imatinib for GIST will be approximately £6.8 million when the number of patients receiving imatinib has reached a steady state.
The resource impact of this guidance on the NHS will depend on the number of patients currently receiving NHS prescriptions for imatinib for the treatment of GIST. Using the assumptions set out in section 6.2, if 25% of eligible patients currently receive NHS prescriptions for imatinib for GIST, the additional cost of implementing this guidance will be approximately £5.1 million. If 75% of eligible patients are currently being treated with imatinib, the impact of the guidance will be less, at about £1.7 million. These estimates are based on a number of assumptions and could be much less if switching to higher doses of imatinib is reduced. The estimates may also be reduced further if GIST patients receive imatinib treatment as a result of the guidance rather than receiving inappropriate surgery or chemotherapy treatment.