DRUG-THERAPY ALTERNATIVES IN THE TREATMENT OF THYROID-CANCER

Therapy of thyroid cancers is based on the removal of the primary dise ase by surgery, replacement of the hormonal deficiencies and subsequen t therapy of the recurrent and metastatic disease. The metabolic chara cteristics of many thyroid tumours mean that radionuclide techniques h ave been used in the identification of sites of tumour and their subse quent therapy. Differentiated thyroid cancers, papillary, follicular a nd mixed papillary follicular, are treated by surgery - usually a tota l or subtotal thyroidectomy, Postoperatively, patients have thyroxine as a replacement therapy and to suppress thyroid-stimulating hormone p roduction. Radioiodine therapy is often given to ablate the thyroid re mnant. This allows (a) adequate follow-up of patients using thyroglobu lin measurements and assessment scans as necessary, and (b) further th erapy with radioiodine for metastatic disease. Patients with a short e ffective half-life of radioiodide may require higher activities or pha rmacological methods of prolonging the retention half-times of iodine, The use of chemotherapy in this group of tumours is limited and at be st provides palliation. The overall prognosis is good for differentiat ed thyroid cancer; papillary carcinomas have an 80 to 90% 10-year surv ival, whereas follicular tumours are associated with a 65 to 75% 10-ye ar survival. Medullary carcinomas map be sporadic or familial, and som e of the latter form part of a multiple endocrine neoplasia syndrome ( MEN). Primary treatment is surgery, and total thyroidectomy is usually recommended since rumours are often multifocal. The use of radiolabel led metaiodobenzylguanidine (MIBG) and In-111 octreotide as potential therapeutic agents has been explored and may be potentially useful in palliative caret Chemotherapy is of limited benefit. The 10-year survi val for medullary carcinomas is 60 to 70%. Anaplastic rumours of the t hyroid are usually aggressive, with a high mortality. Treatment is pal liative by surgical debulking; some patients may benefit from local ra diotherapy or occasionally chemotherapy. The use of therapeutic doses of radionuclides is well tolerated, although it may be associated with a variety of mostly transient adverse effects, including gastritis, t hyroiditis and sialadenitis. Therapy with high activities of radioiodi ne require radiation protection precautions. Despite retreatment with radioiodine there appear to be no long term effects on the fertility o f patients, and healthy children are born to women receiving this trea tment. I-131 remains perhaps the most specific cancer therapy availabl e today and has few adverse effects. II is difficult to see any marked improvement being developed for differentiated thyroid cancer, with t he possible exception of targeted gene therapy.