Introduction

It has been known for many years that two or more independent primary tumors can arise in the same patient. Schoenberg (1977), who surveyed multiple cancers in Connecticut between 1935–1964, appears to have been the first to make a comprehensive quantitative analysis of the risk of developing a second tumor through the investigation of 120, 195 cancer patients from a well-defined population.

Second cancers may arise in the same individual for a number of reasons (Table 59.1). The major issue is usually whether an excess risk represents a common causal factor or some degree of genetic susceptibility. Among relevant issues are the following: (i) the recognition of syndromes of associated sites which may suggest a common etiology; (ii) identification of the regions of the body to which special attention should be paid when following up individuals with the first cancer; (iii) assessment of the carcinogenicity of treatments used for a first cancer.

Common etiological factors

The combined effects of tobacco and alcohol largely account for the constellation of cancers arising in the oral cavity, larynx and oesophagus. In contrast the association between retinoblastoma and osteosarcoma is most likely to reflect the influence of common hereditary factors. The interplay of both exogenous and endogenous factors in multiple cancers of the breast, uterine corpus, ovary and colon has long intrigued investigators. Both reproductive factors and dietary habits are believed to be involved. Biilow et al. (1990) report metachronous colorectal cancers can be as high as 30% after 40 years.