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Over 5,614 TC cases were recorded which included 2,007 males and 3,617 females. The relative frequency of TC in males varied between 0.36% in Dibrugarh and 1.99% in Thiruvananthapuram whereas in females it varied between 0.9% in Dibrugarh and 5.71% in Thiruvananthapuram. An excess of females was seen in all the registries. In most of the registries the histological confirmation was found in 80-95% if cases. Among the registries, a high frequency of TC was observed in the Thiruvananthapuram registry, in both sexes. This phenomenon has been observed in all the years’ data from this registry.

The histological distribution of TC among the hospital registries (27) by sex is shown in (Fig. 1). The percentage of papillary adenocarcinoma though separately reported has been included in PC type. The ‘other’ category includes other carcinoma type, carcinoma NOS and malignant tumors. The proportion of the ‘other’ category was found more in the Dibrugarh registry as compared to the other registries. The relative frequency of PC was the predominant type in all the registries except Dibrugarh where the FC was common in both sexes.

In the Dibrugarh, registry the relative frequency of undifferentiated carcinoma accounted for 10.7% in males and 11.8% in females. These percentages were higher than that reported in other registries.

Pediatric Cancer – Relative Frequency

The occurrence of TC among children (0-14 years) has been reported from hospitals in India. Though its relative frequency is infrequent there are variations among the cases seen from different hospitals in the country. At TMH, Mumbai, in an analysis of 7,057 childhood cancers seen during 1984-94, cancer of the thyroid accounted for 30 cases (0.4%) which included 11 males and 19 females (10). Histological classification of childhood TC cases seen at the TMH showed the predominance of PC (males: 63.6% females: 89.5%) followed by FC (males: 36.3% females: 10.5%) in both sex (10). About 13,387 childhood cancers from six-hospital cancer registries over a ten-year period 1984-93 (27) were reported to the NCRP network which formed about 3.95% of all cancers. This percentage varied between 2% (Dibrugarh registry) to 7.5% (Chandigarh registry). For males and females it varied between 2.9% (Dibrugarh registry and 3.8% Thiruvananthapuram registry). Epithelial cancers in the pediatric group constituted about 2.9% among males and 4.4% among females. Twenty-four males (0.3%) and 39 females (0.8) were diagnosed as having TC among all the childhood cancers from the six registries (27).

Incidence – National Scene

A Mumbai population based cancer registry was established in 1961 and since then cancer incidence for the Mumbai population has been published. In 1964-66 the Age Standardized Rate (ASR) for TC were 0.5 and 0.9 per 100,000 for males and females respectively (16). The ASR in 1993 was 1.0 and 1.9 for males and females respectively (13). With the establishment of the NCRP, by the ICMR, New Delhi, there are at present five urban population based cancer registries in India and one rural registry at Barshi, Sholapur. The other registries mentioned in (Table 5); were either supported by a voluntary organization or by the institutions themselves. The ASR for TC reported from population based cancer registries in India for the year 1991 are shown in (Table 5).

Table 5 : Age adjusted incidence rates per 100,000 of thyroid cancer in India in 1991

Trend

The incidence rates of TC observed in the six registries (13) in India for a six year period from 1988-93 are shown in (Fig.2). Though it is too short a period to analyze the trend, there has been hardly any increase in the incidence over the years in India.

Incidence – International Scene

Cancer incidence in five continents has been reported by the International Agency for Research on Cancer (IARC) in six volumes from 1966 onwards. These reports give the incidence of cancer in several countries around the world for the last 30 years (3,14, 15,29,36,37). The ASR for TC collected from the six volumes for selected countries for males and females are presented in (Fig.3). Among the 60 odd countries reported, USA Hawaii, Hawaiian group (7) showed the highest rate for TC in both sexes. The rates in both sexes in India (Mumbai) though higher than that in the UK (Oxford) in males remained lower than the rates in most of the population groups. Further, the ASRs are higher in females than in males. The increasing incidence has been observed in males and females in the USA, Japan, Finland and Singaporean Chinese populations, whereas in India and the UK the rates remained almost steady. A high incidence of TC has been observed in Iceland and in native Alaskan women (21).

An analysis of incidence data from Connecticut, USA between 1935-39 and 1990-92 indicated that the increase in the incidence was due to cohort effect. The increase was observed in the cohort born between 1915 and 1945 for those born after 1945 the incidence declined. This was attributed to the practice of radiation treatment for benign childhood conditions (42).

Pediatric Cancer – The National and International Scene

Cancer of thyroid in children has been observed and reported from all over the world. Though its frequency is infrequent throughout the world, it has provided a base to study the etiology of this disease. Parkin et al (29) have collected data on children from both population based registries and from established hospitals throughout the world and published a book entitled “The international incidence of childhood cancer”. Over 50 countries had contributed data to this volume, which included regions from Africa, North America (USA and Canada), South American (Brazil, Columbia, Cuba, Jamaica, Puerto Rico), Asia (15 countries), Europe (22 countries) and Oceania (Australia, New Zealand and Fiji). The incidence rates of childhood cancer per million, from a selected population/ countries in the world and also the incidence rate of TC (epithelial) around the world are shown in (Table 6).

The highest ASR’s for TC in children among females were reported from Blacks in Los Angeles, USA with a rate of 2.8 per million and among males from the non Jewish population in Israel at 2.3 per million. Further the ASR’s were higher in females than in males. It was observed in 33 out of the 65 populations reported and the rate in females was about one to five times higher than that in males.

Table 6 : ASR for all pediatric cancer and thyroid cancer for selected countries by sex

The incidence of cancer for the whole country at present is not available due to the lack of countrywide cancer registration. Even existing population based cancer registries cover about 17% of the urban population and less than 1% of the rural population. With these limitations some authors have attempted to estimate the cancer load for the entire country in 2001 both for all sites and for specific sites. The population projection prepared by an expert committee for 2001 (24) indicates that there will be around 1004 million persons of which 30% will be living in urban areas and 70% in rural areas. The estimates of cancer load in India in 2001 (11,13,25,46) for all sites and some specific sites have been provided by some investigators (Table 7). The cancer load would be between 0.566 million (46) and 0.924 million (11). The number of persons with TC in India in 2001 will be around 3,524 (0.6%) (46).