N.A. Jafarey ( Department of Pathology, Basic Medical Sciences Institute, Jinnah Postgraduate Medical Centre, Karachi. )
S.H.M, Zaidi ( Department of Radiotherapy, Jinnah Postgraduate Medical Centre, Karachi. )
The available data on Cancer in Pakistan is based on the records of cases registered in some of the Departments of Radiotherapy and Pathology in the country. The information is thus confined to relative frequency of different tumours. Mortality rates, incidence rates and prevalence rates are not available, except for a snnll population base study done for the prevalence of carcinoma of the oral cavity in some areas of Karachi1. This is not an unusual situation as population based data are not available in most of the countries of the region.
Despite the fact that relative frequency data are not as good as incidence rates, useful information can be extracted from them. In this article the different ways in which the relative frequency data has been used in Pakistan will be described. In the order of presentation these will be:
1. Relative frequency data collected from five centres in the country as a part of a multi-centre study.
2. Comparing of the data collected in the above five centres in 1973-74 with that in 1979-83.
3. Examining the changes in the disease pattern in Jinnah Postgraduate Medical Centre, Karachi over the last 25 years.
PMRC MULTI-CENTRE DATA 1981
Pakistan Medical Research Council supported a study on the frequency of malignant tumours in sewn centres around the country in 1973 which covered a period of 18 months. In 1977 this study was re.started in 5 centres. This study is still continuing. In these studies a uniform recording proforma was used. This reporting card is based on the format recommended by WHO2
Table 1 shows the frequency of different tumours in males and females for the year 1981 which is the year in which census was done. The five centres from which the data is being presented are:
1. Jinnah Postgraduate Medical Centre, Karachi (JPMC). The data from this centre E of a hospital based cancer registry.
2. Uaquat Medical College, Jamshoro (LMC). The data from this centre is of cases registered with the Department of Radiotherapy.
3. King Edward Medical College, Lahore (KEMC). The data from this centre is of cases registered with the Department of Radiotherapy.
4. Armed Forces Institute of Pathology, Rawalpindi (AFIP). The data from this centre is of all histologically proven cases submitted to it from defence service establishments throughout Pakistan plus many of the civilian institutions in Rawalpindi/Islamabad area.
5. IRNUM, Peshawar is a Radiotherapy Institute and the data is of all cases registered with it.
The above five centres are located in different parts of the country giving a fair coverage of the different population clusters in Pakistan. The sources of cases covered by the different centres are however not the same. Three of the centres-LMC, KEMC & IRNUM are only reporting cases which are registered with the Department of Radiotherapy. JPMC is reporting all cases referred to the Department of Radiotherapy plus all histologically proven cases seen in the Department of Pathology which have not already been registered in the Department of Radiotherapy. The fifth centre in the study is AFIP which only reports histologically proven cases. Another difference in the different centres which should be taken note of is the geographical coverage of each centre. JPMC covers mostly Karachi and its surroundings; a population of about 10 million or so. LMC, KEMC and IRNUM receive a large number of cases from the adjoining districts which they serve. AFIP is a referal centre for defence service hospitals throughout Pakistan but gets the bulk of its cases from those living in Rawalpindi/Islamabad area. The degree of bias produced by these differences are difficult to assess, but one study carried out at JPMC comparing the data of the Departments of Radiotherapy and Pathology showed remarkable similarity3.
Table II shows the ten commonest tumours among the males and females in each of the five centres and when all the centres are combined. The differences between different centres and the national or combined figures are better noted when the ranking position of the ten commonest tumours in the combined list are seen for individual centres. This is shown in Table III.
Data collected from 1977 to 1983 was also sent to International Agency for Research in Cancer and is included in the book on “Cancer Occurrence in Developing Countries”4. In the analysis done at IARC the Age Standardized Cancer Ratio (ASCAR) has also been calculated5. This provides a more reliable comparison of the relative frequencies of different tumours in different centres. The ASCAR score for some of the tumour sites in different centres is given in Table IV.
Using the 1981 census figures the crude and Standardized incidence rates have also been calculated at IARC. The incidence rates for some of the common tumours are shown in Table V.
COMPARISON OF 1973-74 & 1981 DATA
As stated above PMRC did a short study on the frequency of malignant tumours in seven centres of the country6. Most of the data in that study was from five of the participating centres so that when the study was restarted in 1977 it included only the five centres reporting large number of cases. The data collected from 1977 to 1980 has been published as a monograph7. Comparing the figures of the two studies some interesting differences have been noted. The most important difference seen was in males where tumours of the Bronchus moved up from the 4th position in 1973-74 to the 1st position in 1977-80 (Table VI).
The relative proportion of the tumours of the Bronchus increased from 7.4% to 9.7%. This increase was not uniform in all centres. There is a South to North gradient which is difficult to explain. In JPMC which is the southern most centre tumours of the Bronchus accounted for 13.6% of all male cases in 1977-80 when at IRNUM and AFIP the two northern most centres it was recorded in only 5.7% of all male cases. A somewhat similar change has been seen in cases of tumours of the Hypopharynx. This site was not in the list of the ten commonest tumours of the males in 1973-74 but occupies the third position in the 1977-80 figures. The cause for the increase in both the tumours of the Bronchus and Hypopharynx are probably the same that is increasing use of cigarettes. While tumours of Bronchus and Hypopharynx have increased those of the Oral cavity have steadily declined. The probable cause of it is the decline in the habit of chewing tobacco. Unlike the males there is no significant difference in the frequency figures of 1973-74 and 1977-80 among the females.
C HANGING TRENDS AT JPMC
At JPMC data on the cases seen since 1959 are available and have been analyzed to note the c hange trends. The relative frequency of various tumours seen over the years were plotted and then the expected values were calculated using the formula for moving averages. The graphs for some selected sites are shown as figures 1-3.
This type of analysis gives some idea of how the relative frequency of any given tumour site varies from year to year. This change does not necessarily reflect changes in the incidence rate of a tumour , but merely how it compares with other cases seen in the same year. Thus, if the incidence of cases from site A increases then the relative frequency of all other tumours will decrease as they are only a proportion of the whole and not rates. Keeping these limitations in mind this type of analysis gives some useful information.
Over the last 25 years there has been consistent fall in the relative frequency of the carcinoma of the Oral Cavity in both the sexes (Figure 1). There has been a lesser degree of reduction in the relative frequency of tumours of the Pharynx and Larynx. On the other hand there has been a steep increase in the relative frequency of tumours of the Bronchus particularly in males (Figure 3) and Esophagus in both sexes (Figure 2).
1. Jafarey, N.A. and Zaidi, S.H. Carcinoma of the oral cavity and oropharynx in Karachi (Pakistan); An appraisal. Trop. Doct., 1976;6: 63.
2. Maclennan, R., Muir, C., Steinitz, R. and Winkler, A. Cancer registration and its techniques: Lyon, International Agency for Research on Cancer, 1978.
3. Jafarey, N.A. and Zaidi, S.H.M. Frequency of malignant tumours in Jinnah Postgraduate Medical Centre, Karachi. JPMA., 1976; 26:57.
4. Parkin, D.M. Editor. Cancer Occurance in Developing Countries. International Agency for Research on Cancer, Lyon, 1986.
5. Tuyns, A. J. Studies on cancer relative frequencies (ratio studies); a method for computing an age-standardized cancer ratio. Int. J. Cancer, 1968;3: 397.
6. Pakistan Medical Research Council :Collection of data of various types of tumours in Pakistan. Karachi, PMRC, 1977.
7. Pakistan Medical Research Council : Malignant tumours. Report of a multicentre study. Karachi, PMRC, 1982.