VOLUME XXXI APRIL, 1931 No. 2 THE INCIDENCE OF CANCER OF THE BLADDER AND PROSTATE IN CERTAIN OCCUPATIONS. BY S. A. HENRY, H.M. Medical Inspector of Factories, N. M. KENNAWAY AND E. L. KENNAWAY. (From the Cancer Hospital Research Institute, London.) CONTENTS. PAGE I. Material examined 125 II. Sources of error 126 III. Method of calculation 128 IV. Incidence of cancer of the bladder 129 V. Occurrence of tumours of the skin, and of the bladder, in the same person 133 VI. The relations between cancers of the scrotum, of other parts of the skin, and of the bladder 134 VII. Incidence of cancer of the prostate . .135 VIII. Cancer of the bladder and prostate in chemical workers .... 136 IX. Summary 136 I. MATERIAL EXAMINED. THE results given below are derived from an examination of death certificates of cases of cancer and papilloma of the bladder in both sexes, and of cancer of the prostate, from England and Wales between 1921 and 1928. The total numbers of certificates examined are shown in Table I; from the whole series of 13,965 cases those relating to cancer of the bladder in males, and cancer of the prostate, Table I. Death certificates examined. Cancer of Papilloma of Cancer of bladder bladder prostate Males. 1921 589 86 — 1922 641 109 — 1923 647 114 — 1924 711 115 1022 1925 745 115 1116 1926 723 134 1145 1927 753 151 1172 1928 812 150 1353 5621* 974 5808* Females. 1924 350 — 1925 337 46 1926 340 51 1927 384 54 1411 151 * The difference between these totals and those given in Table II is due to the exclusion from the latter Table of seven cases of cancer of the bladder, and four cases of cancer of the prostate, occurring in persons under 20 years of age. Journ. of Hyg. xxxi 9 Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 02 Oct 2021 at 10:53:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0022172400010731 126 Cancer and Occupation numbering 11,429, were chosen for study in detail, as in these classes the largest numbers and the best occupational data are available. The two classes which were not used for exact tabulation of the occupations, namely, papilloma of the bladder, and cancer of the bladder in females, were put aside for the following reasons: (a) The cases of papilloma, which amount to little more than one-sixth of those of cancer of the bladder, are insufficient in number; but data were obtained from this series, in regard to the chemical trades especially, which will be studied in future when more figures are avail- able. This class is valuable because the proportion of correct diagnoses is pro- bably high and the inclusion of any prostatic or rectal tumours is unlikely. (b) The death certificates of women did not yield a sufficient number in which any industrial occupation was recorded. Thus, in 1925, only 15 of the 337 death certificates for cancer of the bladder in women recorded any occupation not connected with domestic, nursing or teaching work. II. SOURCES OF ERROR. The analysis of such material as is afforded by the 11,429 certificates of cancer of the bladder in males, and of the prostate, encounters many difficulties, which may be classified under three headings. First, it is necessary to know the total number of persons following any given occupation. This is learned from the Census results (in this case the Census of 1921) but (1) the figure given by the Census cannot be relied upon throughout the 10 years until the next Census; (2) the utility of the Census figures in the present investigation depends upon the possibility of obtaining in the death entries such detailed information in regard to occupation and in- dustry as would enable the resultant figures to be related to the Census figures. It was not possible for example to ascertain a population at risk in regard to certain workers in chemicals and chemical manufactures in whom we were interested, and the corresponding death certificates, from which very inte- resting results might have been expected, could not be used statistically. Second, with regard to the smaller occupations. Some of the most inte- resting from the present standpoint (patent fuel manufacture, tar distilling, chimney sweeping) employ a few thousand men only, who will yield but very few cases of cancer of the bladder even if the incidence is high. Hence the sampling error will be large even over a period of 8 years. Three of the four deaths of tar distillers from cancer of the bladder recorded in Table III occurred in two of the eight years (1922 and 1923). Third, with regard to the individual entry in the death register. (1) This gives no information about the length of time during which the deceased followed the occupation named. (2) In some cases, especially in the case of deaths occurring in institutions, the information available to the Registrar at the time of registration is not so detailed as that supplied by the man him- self at the Census. (3) Incorrect diagnosis is of course a possible source of error which is unavoidable in all such material. Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 02 Oct 2021 at 10:53:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0022172400010731 S. A. HENRY, N. M. KBNNAWAY AND E. L. KBNNAWAY 127 In the work recorded here, an attempt has been made to avoid these in- accuracies by special enquiry into individual cases in some occupations (patent- fuel labourers, gas-works engine and crane drivers, gas fitters, gas stokers, gas- works inspectors and foremen, gas workers and labourers (not stokers), gas- producer men, coke-oven workers, brick kiln and oven men, blast f urnacemen and labourers, dye mixers and dyers) where the smallness of the number employed made an error in a single death certificate most serious. Such enquiry was made in fifty cases of cancer of the bladder, chiefly of the more recent years (1924- 1928), from relatives, fellow-workmen and employers of the deceased, with re- ference especially to the exact nature of the occupation and the length of time for which it had been pursued. Of these fifty cases, forty-four could be traced. In forty-one the reliability for our purpose of the information given on the death certificate was confirmed. In one case the short time for which the occupation had been followed (5 to 6 months) caused it to be rejected as a factor, although the entry was of course perfectly correct. In two cases the industry rather than the occupation in that industry had been recorded. Thus an "alkali labourer" was found to have worked for 32 years at a gas-producer plant, and the case was transferred accordingly to the class of gas-producer men. The minimum duration of exposure necessary to produce an occupational cancer cannot be stated, and this question is a constant source of difficulty in such work as is presented here. In this series we have rejected the case of a gas- works labourer who had been employed in that work for not more than 5 or 6 months before death, and have retained the cases of a dyer with 2 years' and of a gas-producer man with 5 years' duration of employment before death. The objection may be raised that if special enquiry be made into any of the cases in Table III it should be made into all. But (1) to investigate, in places scattered all over England and Wales, the accuracy of over 1400 death certificates was not practicable for us. (2) The risk of serious error is greatest in the smaller groups. Thus, if the certificate relating to one of four patent-fuel labourers is incorrect, the error is serious; but it is extremely unlikely that 25 per cent, of the 160 farmers are described incorrectly. (3) The comparatively small number of occupational terms in some of the larger groups causes less classification difficulty in those groups than in some of the smaller ones. Thus, an agricultural labourer can hardly be misnamed, whereas a tar distiller may be described as a by-product worker, or a stillman in a chemical works. The occupational classification in use at the General Register Office was revised in 1921. The change was made in accordance with a resolution of the British Empire Statistical Conference of 1920 in favour of separate and inde- pendent tabulations by occupation and by industry. The classifications used in 1911 and earlier were only in part occupational, being largely industrial in nature. The change precludes the possibility of an exact comparison with previous Census results (see General Report, Census of England and Wales, 1921, p. 86), or with the data on the occupational incidence of cancer in England and 9-2 Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 02 Oct 2021 at 10:53:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0022172400010731 128 Cancer and Occupation Wales in 1910, 1911 and 1912, published by the Medical Research Council (Young, Russell, Brownlee and Collis, 1926). In the last-named report the occupations associated with coal gas, tar and pitch, do not appear in the tables devoted to cancer of the bladder and prostate.