In thyroid cancers the thyroid functions are usually normal and there is no raise of the T3 and T4. Despite that weight loss can occur because any cancer in the body causes a catabolic state (negative metabolism). This is responsible for the loss of weight. Any malignant process in the body has a constitutional symptom in the form of loss of appetite also. This also is many times is a factor for the weight loss.
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Any malignant process in the body can cause tiredness also. But all these symptoms are reversible and once the nodule is excised these symptoms would cease to exist. The papillary cancer of the thyroid has an excellent prognosis and is considered as treatable cancer.
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