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Neuroendocrine tumors (NETs) of the distal colon and rectum are also known as hindgut carcinoids based on their common embryologic derivation. Their annual incidence in the United States is rising, primarily as a result of increased incidental detection. Symptoms of rectal NETs include hematochezia, pain, and change in bowel habits. Most rectal NETs are small, submucosal in location, and associated with a very low malignant potential. Tumors larger than 2 cm or those invading the muscularis propria are associated with a significantly higher risk of metastatic spread. Colonic NETs proximal to the rectum are rarer and tend to behave more aggressively. The incidence of rectal NETs in African Americans and Asians is substantially higher than in Caucasians. Colorectal NETs are generally not associated with a hormonal syndrome such as flushing or diarrhea. A multidisciplinary approach is recommended in diagnosing and managing hindgut NETs.

Summary Background Chemotherapy has historically proven ineffective in advanced differentiated thyroid cancers, but the realisation that various tyrosine kinases are activated in the disease suggested a potential therapeutic role for tyrosine-kinase inhibitors. We investigated the safety and efficacy of pazopanib. Methods This phase 2 trial was done from Feb 22, 2008, to Jan 31, 2009, in patients with metastatic, rapidly progressive, radioiodine-refractory differentiated thyroid cancers. Each patient received 800 mg continuous pazopanib daily in 4-week cycles until disease progression, drug intolerance, or both occurred. Up to two previous therapies were allowed, and measurable disease with radiographic progression in the 6-month period before enrolment was a requirement for inclusion. The primary endpoint was any tumour response, according to the Response Evaluation Criteria in Solid Tumors 1.0. This study is registered with ClinicalTrials.gov, number NCT00625846. Findings 39 patients were enrolled. One patient had received no previous radioiodine therapy and another withdrew consent before treatment. Clinical outcomes could, therefore, be assessed in 37 patients (19 [51%] men, median age 63 years). The study is closed to accrual of new patients, but several enrolled patients are still being treated. Patients received a median of 12 cycles (range 1 to >23, total >383). Confirmed partial responses were recorded in 18 patients (response rate 49%, 95% CI 35–68), with likelihood of response lasting longer than 1 year calculated to be 66%. Maximum concentration of pazopanib in plasma during cycle one was significantly correlated with radiographic response (r=−0·40, p=0·021). 16 (43%) patients required dose reductions owing to adverse events, the most frequent of which (any grade) were fatigue (29 patients), skin and hair hypopigmentation (28), diarrhoea (27), and nausea (27). Two patients who died during treatment had pre-existing contributory disorders. Interpretation Pazopanib seems to represent a promising therapeutic option for patients with advanced differentiated thyroid cancers. The correlation of the patient’s response and pazopanib concentration during the first cycle might indicate that treatment can be individualised to achieve optimum outcomes. Assessment of pazopanib in an expanded cohort of patients with differentiated thyroid cancer, as well as in cohorts of patients with medullary and anaplastic thyroid cancers, is presently being done. Funding National Cancer Institute, supported in part by NCI CA15083 and CM62205.

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