Understanding of neuroendocrine tumors (NETs) has rapidly evolved over the past several years. With this new knowledge, diagnoses have increased over the past few decades. NETs are thought to arise from cells in the diffuse neuroendocrine system throughout the body. Typically, they are well-differentiated and grow more slowly than many other tumor types. In many cases, NETs are resistant to standard cytotoxic chemotherapy. Although most are nonfunctional, NETs have the ability to secrete neuropeptides that may result in symptoms of hormone hypersecretion (functional).
A current estimate of NET prevalence is 103,312 individuals in North America, which is higher than that of many other gastrointestinal tumors, including esophageal, pancreatic, gastric, and hepatobiliary cancers.
Most NETs are well-differentiated, but the histology of these tumors has a broad spectrum, explained Matthew H. Kulke, MD, MMSc, Director, Neuroendocrine and Carcinoid Tumor Program, Dana-Farber Cancer Institute, at the NCCN 22nd Annual Conference. Classification of NETs is based on differentiation and grade, he continued. Well-differentiated tumors are either low-grade (grade 1) or intermediate-grade (grade 2); although poorly differentiated tumors are generally considered grade 3. Grade 2 tumors tend to be more aggressive than grade 1, and the prognosis is better for grade 1 tumors than for grades 2 and 3. “The classification scheme continues to be debated,” and may be updated in the next few years, he said.
For example, a study of 252 patients with poorly differentiated NETs (grade 3) treated with platinum/etoposide found that tumors with a Ki-67 index >55% had a much higher response rate.1 Thus, the >55% cutoff for Ki-67 may be more appropriate for poorly differentiated tumors when considering treatment selection, Dr. Kulke noted. Tumors with a Ki-67 index <55% may respond more favorably to treatment described for well-differentiated tumors.
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