Chimney sweeps' carcinoma
Chimney sweep's cancer, also called Soot wart, is a squamous cell carcinoma of the skin of the scrotum. It has the distinction of being the first reported form of occupational cancer, and was initially identified by Percivall Pott in 1775. It was initially noticed as being prevalent amongst chimney sweeps.
Chimney sweeps' carcinoma is a squamous cell carcinoma of the skin of the scrotum. Warts caused by the irritation from soot particles, if not excised, developed into a scrotal cancer. This then invaded the dartos, enlarged the testicle, and proceeded up the spermatic cord into the abdomen where it proved fatal.
Chimney sweeps' carcinoma was first described by Percivall Pott in 1775 who postulated that the cancer was associated with occupational exposure to soot.  The cancer primarily affected chimney sweeps who had been in contact with soot since their early childhood. The median age of onset of symptoms in one review was 37.7 years, although boys as young as 8 years old were found to have the disease. It was proposed by W.G. Spencer in 1890 that sweat running down their bodies had caused soot to accumulate in the rugae of the inferior surfaces of the scrotum, with the resulting chronic irritation causing scrotal cancer,  but this was shown to be an incorrect artifact of the method used to stain his microscope slides.
In 1922, R.D. Passey, a research physician at Guy’s Hospital in London produced malignant skin tumors in mice exposed to an extract made from soot, demonstrating the presence of carcinogenic substances in soot which were the likely cause of cancer of the scrotum in chimney sweeps. 
in the 1930s Ernest Kennaway and James D. Cook of the Research Institute of the Cancer Hospital, London, (later known as the Royal Marsden Hospital) discovered several polycyclic hydrocarbons present in soot that were potent carcinogens: 1,2,5,6-dibenzanthracene; 1,2,7,8-dibenzanthracene; and 1,2-benzpyrene (3) benzo[α]pyrene. DNA consists of sequences of four bases - adenine, thymine, cytosine and guanine - bound to a deoxyribonucleic backbone. Benzo[α]pyrene interacts with deoxyguanosine of the DNA, damaging it and potentially starting the processes that can lead to cancer.
The disease was principally a British phenomenon; in Germany, for example, sweeps wore tight-fitting protective clothing which prevented the soot from accumulating on the lower surface of the scrotum, whereas boys in the UK were once sent up the chimneys wearing only trousers and shirt, and occasionally naked. In the United Kingdom before the flexible brush was introduced, the master sweeps took apprentices, who were boys from the workhouse or bought them from their parents and trained them to climb chimneys. In the German States, master sweeps belonged to trade guilds and did not use climbing boys. In Italy, Belgium, and France climbing boys were used. Boys as young as four climbed hot flues that could be as narrow as 230 mm square. Work was dangerous and they could get jammed in the flue, suffocate or burn to death. The boys slept under the soot sacks and were rarely washed. From 1775 onwards there was increasing concern for the welfare of the boys, and Acts of Parliament were passed to restrict, and in 1875 to stop this usage. Lord Shaftesbury, the philanthropist, led the later campaign. In the United States, black children were hired from their owners and used in the same way, and were still climbing after 1875.
Sir Percivall Pott
Sir Percivall Pott (6 January 1714 – 22 December 1788) London, England) was an English surgeon, one of the founders of orthopedy, and the first scientist to demonstrate that a cancer may be caused by an environmental carcinogen. In 1765 he was elected Master of the Company of Surgeons, the forerunner of the Royal College of Surgeons. It was in 1775 that Pott found an association between exposure to soot and a high incidence of chimney sweeps' carcinoma, a scrotal cancer (later found to be squamous cell carcinoma) in chimney sweeps. This was the first occupational link to cancer, and Pott was the first person to demonstrate that a malignancy could be caused by an environmental carcinogen. Pott's early investigations contributed to the science of epidemiology and the Chimney Sweepers Act 1788.
Pott describes chimney sweeps' carcinoma thus:
It is a disease which always makes it first attack on the inferior part of the scrotum where it produces a superficial, painful ragged ill-looking sore with hard rising edges.....in no great length of time it pervades the skin, dartos and the membranes of the scrotum, and seizes the testicle, which it inlarges(sic), hardens and renders truly and thoroughly distempered. Whence it makes its way up the spermatic process into the abdomen.
He comments on the life of the boys:
The fate of these people seems peculiarly hard ... they are treated with great brutality ... they are thrust up narrow and sometimes hot chimnies, [sic] where they are bruised burned and almost suffocated; and when they get to puberty they become ... liable to a most noisome, painful and fatal disease.
Though Pott wrote no further papers on the subject, clinical reports began to appear suggesting that others had seen it without realising what it was and like Pott had said:
[ as it occurs after puberty]....it is generally taken, both by patient and surgeon for venereal and treated with mercurial [salts].
The disease was usually preceded by the development of hyperkeratotic lesions on the scrotum, which was what the sweeps called soot warts. These could be benign; sweeps often removed them themselves by trapping them in a split cane and cutting them off with a pocket knife. For instance:
"he... seized with a split stick and cut off with a razor. He remarked that it was not very painful. He resumed work the following day."
But if the lesion had become malignant it was far more serious. Patients frequently delayed seeking medical opinion, and when they did many were in a dreadful state. A 28-year-old sweep approached Jefferies in 1825, who describes his condition:
"The sore occupies the whole of the left side of the scrotum and the inner angle of the thigh, extending from the anus to the posterior inferior spinous process of the ileum, presenting a surface as large as a man's open hand, with hard indurated edges and irregular margins, discharging a thin sanies, which is extremely offensive; the left testicle is entirely denuded, and projects from its centre; in the left groin is a mass of indurated glands, the size of a goose's egg, which appears to suppurate in the right groin: there is likewise an ulceration, of the same malignant nature, about the size of a half-crown (5 cm). . ." Despite the appearance of this growth, the unfortunate man was in no pain and his only complaint was that about 10 days before his admission he had bled from his groin and lost about a pint of blood. Even this, however, had not unduly affected his constitution.
Treatment was by surgery, where all the diseased flesh was cut out. Before the introduction of anaesthetics this was a simple process for the surgeon but terrifying for the patient. Alternative treatments were also proposed including the application of an arsenic paste poultice. The real cause of this cancer was unproved until the discovery of weak carcinogens in soot by Passley in 1922. Until then the most popular theory was that soot got trapped in the rugae of the scrotum and this caused a general irritation. Sweeps were not known for their attention to bodily hygiene and it was assumed they never washed their genitals. The youngest victim, recorded in 1790 by James Earle (Pott's son-in-law), was 8 years old.
Decades later, it was noticed to occur amongst gas plant and oil shale workers, and it was later found that certain constituents of tar, soot, and oils, known as polycyclic aromatic hydrocarbons, were found to cause cancer in laboratory animals. The related cancer, mule spinners' carcinoma, was blamed on the carcinogenic content of shale oil that was used to lubricate the rapidly revolving mule spindles.
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