Usually NOT. It may infrequently produce antibodies that make it less effective, but this is in only a very small minority of cases. In some other cases it becomes less effective AT THE SAME DOSAGE because the tumors are growing. In most cases it is better to take it early in the disease, especially if carcinoid syndrome is present and blood serotonin levels are elevated because it will prevent carcinoid heart disease and inhibit tumor growth as well as prevent carcinoid syndrome symptoms
