Investigating thyroid cancer

Diagnosis of thyroid cancer has seen radical changes over the last few years. Economical and painless outpatient procedures now allow a precise diagnosis, says Prof. N. DORAIRAJAN.

THE thyroid gland is an inconspicuous butterfly shaped endocrine gland situated in the neck. Although small, it plays a vital role in normal mental development, growth and reproduction. Cancer of this gland has become more common in recent years. It has been reported that cancer of this gland forms the commonest type (65 per cent) occurring in the endocrine system. It also accounts for one per cent of all body cancers. This can affect an individual of any age group, even children less than 10 years. Even though it affects women predominantly in a ratio of 3:1, men are not altogether spared.

Among the factors that cause an increased incidence of this cancer is the effect of radiation. The survivors of the Hiroshima and Nagasaki bombings had a very high rate of thyroid cancer. In the 10 years following the Chernobyl disaster, of every 1000 inhabitants exposed to this accident, 62 developed it. Today, this tumour occurs more commonly among those who have been exposed to radiation as children.

In India, thyroid cancer has a widespread distribution with certain subtypes, notably papillary cancer, occurring in coastal areas of Tamil Nadu, Andhra Pradesh and Kerala which are iodine rich. The iodine content of soil modifies development of these cancers.

The medullary subtype cancer, which forms 3-5 per cent of all thyroid cancers, is now known to be hereditary. This cancer, inherited as an autosomal dominant trait, occurs in the syndromes of familial medullary cancer and Multiple Endocrine Neoplasia (MEN). The papillary subtype is also reported to be hereditary.

There are, however, several definitive indicators which provide an insight to the final outcome. A higher cure rate is seen in women below 40 years, in the absence of local spread of cancer and if the swelling is less than four cm in diameter. This prognostic system has widely come to be known as the AMES prognostic system.

Iodine is a trace element ingested in inorganic form and converted into the organic form in the thyroid gland. Iodine content in the diet has been linked to varying patterns and development of thyroid cancer. The presence of large goitre belts in the United States, led to an experiment in the 1920s in which school girls were given iodine supplements. As a result, there was a marked decrease in the incidence of goitre. The follow-up showed that these girls suffered from a lower incidence of aggressive thyroid cancers compared to the general population. Further in those who developed cancer, it was curable. Moreover, there was a decrease in the evidence of follicular cancer.

Many who migrated from iodine poor regions to iodine rich regions showed decreased trends of development of follicular cancer. In South India, excess iodine in diet is related to the higher incidence of papillary cancer compared to other more malignant subtypes of thyroid cancer. Thus, iodine has a protective effect in the development of a more curable form of thyroid cancer.

Shellfish and other seafood which form the staple diet in countries like Iceland and Norway are associated with the highest incidence of thyroid cancer in the world. In women, certain factors such as the size of the family, the use of oral contraception, late age of first childbirth (above 30 years) are said to constitute an increased risk.

Although thyroid cancer is not preventable, avoiding exposure to radiation during childhood and screening for cancer in susceptible families go a long way in early diagnosis and cure. In families affected by the medullary subtype, bio-chemical and genetic screening has resulted in early detection. Calcitonin, a hormone produced by 'C' cells in the thyroid gland (from which this type of cancer arises) can be considered a marker. Genetic screening for the RET proto-oncogene further helps to confirm the risk of developing this cancer.

Ultrasound of the thyroid, if done properly, can pick up millimetre sized nodules in the thyroid and ultrasound-guided fine needle aspiration cytology (FNAC)" is an useful screening procedure.

The presence of a swelling in the neck needs further evaluation. In young girls, the swelling may be a physiological manifestation which is resolved in time, but still needs to be evaluated in order to rule out underlying cancer. If the swelling moves upwards on swallowing, change in voice, difficulty in swallowing or breathing signifies advancing disease. In families predisposed to thyroid cancer, regular checkup and a genetic study is necessary. Today with the advent of modern diagnostic facilities such as FNAC, a diagnosis readily obtained. It is a reliable, effective and relatively painless outpatient procedure done without anaesthesia. The result can be obtained immediately and the test can be repeated four or five times if necessary.

In patients affected by medullary thyroid cancer and in those showing RET oncogene positivity, 90 per cent develop medullary carcinoma. Prophylactic surgery, involving removal of the thyroid gland before cancer develops, is common today. Patients can live normally after surgery but have to take thyroxine tablets as replacement therapy.

For other thyroid cancers, the patient needs surgery at the earliest. Early surgery is safe and the results are good. The papillary subtype of thyroid cancer is curable. If diagnosed early, the patient can live normally. In advanced cases, treatment becomes difficult and surgery, if possible, is done. Otherwise palliative radiotherapy is required.

The writer is a Professor of Principles and Practice of Surgery, Madras Medical College and Research Institute and Consultant, Endocrine Surgeon, Apollo Hospitals, Chennai.

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