Describe the occupational cancers.

Occupational Cancers

• Their historical significance deserves the opening of any answer — percivall POTT’S description of scrotal cancer in chimney sweeps in 1775 was the first identification of an occupational carcinogen and one of the first of any environmental cause of cancer
• The pattern has repeated since — the occupational setting, with its high doses and defined cohorts, revealed asbestos, VINYL chloride, benzene and aromatic amines as carcinogens long before their effects at lower doses in the general population could have been detected
• Occupational epidemiology has therefore served as an early warning system for the whole population, which is an argument for studying it even where the number of workers is small
• The characteristics of occupational cancer:
• Long latency, typically 15 to 40 years, so that the cancer appears long after the job has been left and often after retirement
• The disease is clinically and histologically identical to the same cancer arising from other causes, so the occupational origin can never be established from the tumour itself and depends entirely on the exposure history
• That single fact explains why occupational cancer is so profoundly under-recognised — a lung cancer in a retired asbestos worker who also smoked will be attributed to the smoking unless someone asks the question
• There may be a dose-response relationship, and for many carcinogens NO safe threshold
• Certain cancers occur at an unusually young age or at an unusual site, which is a clue
• Synergism with other exposures, particularly smoking, is common
• The important agents and their target organs should be learned as pairs, since that is how they are examined:
• Asbestos → mesothelioma (pleural and peritoneal), lung cancer, and laryngeal and ovarian cancer
• Mesothelioma is virtually pathognomonic of asbestos exposure, which makes it the one occupational cancer that announces its own cause
• Aromatic amines — benzidine, beta-naphthylamine, aniline dyes → bladder cancer, in dye, rubber and leather workers
• Benzene → leukaemia and aplastic anaemia, in petrochemical, painting, shoe and rubber industries
• VINYL chloride monomer → angiosarcoma of the liver, a tumour so rare that a handful of cases in one plant was sufficient to establish the association
• Arsenic → skin, lung and bladder cancer
• Chromium and nickel → lung and nasal sinus cancer
• Wood dust → nasal and paranasal sinus adenocarcinoma, in furniture makers
• Leather dust → nasal cancer
• Polycyclic aromatic hydrocarbons, soot, tar and pitch → skin and scrotal cancer and lung cancer
• Ionising radiation → leukaemia, thyroid, lung and bone cancer
• Radon in mines → lung cancer
• Ultraviolet radiation in outdoor workers → skin cancer
• Silica → lung cancer
• Cadmium → lung and prostate; and formaldehyde → nasopharyngeal cancer and leukaemia
• The IARC classification should be mentioned — group 1 (carcinogenic to humans), 2A (probably), 2B (possibly), 3 (not classifiable) and 4 (probably not)
• The classification concerns the strength of the evidence that a substance can cause cancer, not the magnitude of the risk it poses — a distinction very widely misreported, since it means that a Group 1 agent may present a small risk at ordinary exposures
• Prevention — elimination or substitution, which is the only fully effective measure since there is often no safe threshold; enclosure and engineering control; strict exposure limits and monitoring; prohibition of the most dangerous agents, as with benzidine; smoking cessation, given the multiplicative synergism; medical surveillance, including of former workers, since latency exceeds employment; and maintaining exposure registers that outlive the employment
• The register point is practically important — a worker who develops mesothelioma thirty years after leaving a factory cannot obtain compensation without a record that they worked there and were exposed
• The tumour never reveals its cause, only the history does, which is why occupational cancer is so profoundly under-recognised
• Keep exposure registers that outlive employment, since a worker cannot prove exposure thirty years later without one
• Mesothelioma announces its own cause, being virtually pathognomonic of asbestos exposure
• Pott described scrotal cancer in sweeps in 1775, which was the first occupational carcinogen ever identified