Module 3: Toxicology - Section 13: Occupational Carcinogenesis

TOX 13.1: Introduction

INTRODUCTION

Background and history of Occupational cancer

The ILO Encyclopaedia has an excellent chapter on occupational cancer which covers all aspects of this topic.

The first recorded occupational cancer was an observation of increased scrotal cancer in chimney sweeps, described by a U.K. surgeon, Sir Percival Pott, in 1713. In 1918, two Japanese scientists showed in lab experiments for the first time that non-biological substances (coal tar) could induce cancer (skin) in animals.

The International Agency for Research on Cancer is the main body conducting evaluation of chemicals and other agents thought to cause cancer. It has produced a very useful classification of these agents in terms of their carcinogenic potential. Around 20 agents and mixtures are established (Group 1) as occupational carcinogens with a similar number suspected as being probably carcinogenic for humans (Group 2A).  Other catetgories of occupational carcinogens include pesticides and drugs during manufacturing or application/administration and environmental agents.

There are an estimated 70 000 chemicals in commercial production, about 1 000 - 3 000 new chemicals per annum. Of these 7000 have been tested in animals. Approximately 1 000 of these are tumerogenic. IARC has evaluated 7913 as of 1993.

Attributability of cancer to occupation

Estimates of the contribution occupational exposures to observed cancers vary widely. In the US there are 430 000 cancer deaths annually.  The proportion of all cancers attributable to occupation has been the subject of considerable debate and ranges from 2 - 8% .  This proportion is higher (up to 40%) when only cancers in exposed worker populations are considered.

PATHOGENESIS OF CARCINOGENICITY:

Characteristics of Cancer:

Some characteristics of cancer may actually be found in benign cell growth as well.

1. Abnormal regulation of cell growth
   • Hyperplasia: increase in cell number
   • Hyperproliferation: increase in cellular growth rate
   • Hypertrophy: increase in cell size
2. Disordered growth
   • Abnormal regulation of cell growth· Metaplasia: replacement of one mature type of cell with another cell type
   • Dysplasia: change in cell arrangement
   • Anaplasia: change of organisation of cells in tissue or organelles within cell
   • Apoptosis loss: loss of programmed cellular death
3. Abnormal differentiation
   • Growth of primitive or undifferentiated cells
   • Altered cellular products
   • Presence of cellular markers (surface proteins) of embryonic or stem cell origin

REFERENCES: 

IARC classification of carcinogenic agents (as at September 2007)

1. ILO Encylcopaedia 4th Edition (1998) Chapter on Cancer:  Introduction.  N Pearce, P Boffeta, M Kogevinas. 
    Pages 2.2. Vol 1.

2. ILO Encylcopaedia 4th Edition (1998) Chapter on Cancer:  Environmental cancer.  BK Armstrong, P Boffeta.  Pages 2.8.  Vol 1.

3.  ILO Encylcopaedia 4th Edition (1998) Chapter on Cancer:  Prevention.  P Gustavsson.  Pages 2.14.  Vol 1.

4.  ILO Encylcopaedia 4th Edition (1998) Table 2.2  : Estimated proportions of cancer attributable to occupation.
   

Another is the website of NIOSH occupational cancers

A useful reference is the website of the US National Cancer Institute  

 

 

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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