Life Threatening Gastrointestinal Tumour More Common Than Suspected
The incidence of gastrointestinal stromal tumours (GISTs), generally considered a rare sarcoma, is more than three times as high as previously believed, according to data presented in Nice at the 27th annual European Society of Medical Oncology (ESMO) Congress. An accurate estimate of GIST incidence has been elusive because of diagnostic ambiguities, now largely resolved by modern immunohistochemistry.
The higher incidence of GIST – calculated at 16 per 1,000,000 people annually – is especially significant because there is now an effective treatment for GIST, the oral therapy imatinib, formerly known as STI 571. The availability of an effective therapy makes it vital to accurately diagnose the disease.
The study, the first population-based examination of the incidence of GIST, was presented by a team headed by Lars-Gunnar Kindblom, MD, PhD, of Sahlgrenska Academy at Göteborg University, Sweden. The team analyzed the medical records and tissue blocks of patients seen from 1983 to 2000 and found 400 cases of true GIST. This was more than three times as many as originally diagnosed. The reanalysis relied in large part on CD 117 (Kit) immunohistochemistry, which Dr. Kindblom pioneered over the past three years. He recommended wider use of CD 117 (Kit) staining for gastrointestinal tumours. Kit receptors in these tumours are the telltale signs of GIST.
“GIST is much more common than we thought, and it is crucial to get the diagnosis right,” Dr. Kindblom said. “Surgeons and pathologists should know that GIST incidence is greater than they had suspected. There is striking variability in the appearance of these tumours, and CD 117 stains for Kit receptors should be widely applied to provide physicians and patients with the best tumour-specific diagnoses, leading to targeted therapeutic options.”
Dr. Kindblom noted that many of the patients in his team’s population-based study who are still living have become candidates for treatment with imatinib.
Historically, GIST has been extremely difficult to treat because of its resistance to treatment with chemotherapy and radiation therapy; surgery to remove GISTs is considered palliative. Imatinib is a targeted treatment for Kit-positive GIST. Imatinib was approved in May 2002 in the European Union, and is also available in many other countries worldwide for the treatment of patients with Kit (CD 117)-positive unresectable (inoperable) and/or metastatic malignant GISTs. An annual incidence of 16 per 1,000,000 means nearly 1,000 new GIST cases per year in France, or about 4,000 new cases per year in the U.S.
The study owes its existence not only to the recent development of CD 117 staining for Kit receptors by Dr. Kindblom but also to the organization of the medical system in southwestern Sweden, where 1.5 million people live. In that part of Sweden, all histology analyses of sarcomas are done in just four laboratories, making their reanalyses manageable.
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