Evaluation of surgical results and prediction of prognosis in patients with medullary thyroid carcinoma by analysis of serum calcitonin levels

Serum calcitonin levels before (S1) and after (S2) surgery were measured in 67 patients with medullary thyroid carcinoma and the patients were followed with serial calcitonin measurements for a mean duration of 7 years. The calcitonin doubling time (T2) was calculated in patients with elevated postoperative calcitonin levels. Assuming that the serum calcitonin level is linearly correlated with tumor weight, the residual tumor weight (W2) is estimated as W1S2/(S1−S2) where W1 is the weight of the resected tumor. The reduction index (α) is defined as W2/(W1+W2)=(1/2)α.αT2indicates the expected prolongation in survival (EPS) by surgery. The survival index (β)is defined as the number of doublings of residual tumor until it weighs 1,000 g, which would generally kill the host. The expected duration of survival (EDS) after surgery is estimated asβT2.Death within 3 years after surgery or recurrence within 5 years was best associated with short EPS followed by short T2 or smallα.S2had a rather weak correlation and S1had almost no correlation with the prognosis. The duration of survival in 3 patients who died of the disease was very close to the EDS. T2indicates growth rate of the tumor,αindicates degree of radicality of the surgery, EPS indicates the effects of the surgery, and EDS indicates duration of survival after surgery. These parameters allow quantitative judgment of the effect of surgery and quantitative prediction of the prognosis in each patient.