CANCER SURVIVAL AND THE DURATION OF SYMPTOMS - AN ANALYSIS OF POSSIBLE FORMS OF THE RISK-FUNCTION

The time interval between onset of symptoms and the diagnosis of cance r [symptom to diagnosis interval (SDI), or duration of symptoms] is a highly complex variable reflecting patient behaviour, the clinical cou rse, the functioning of the health system and tumour biology. In order to assess possible forms of the risk function of SDI upon cancer surv ival whilst taking into account the effects of age, sex, tumour site a nd stage at diagnosis, 1887 symptomatic cases of lung, breast, stomach , colon, rectal, bladder cancer and lymphomas registered in the Tumour Registry of the Hospital del Mar (Barcelona) were analysed by means o f survival curves and Cox proportional hazards regression. Subjects (m ean age 64 years) were followed for a median length of 15 months after diagnosis (follow-up rate 93.5%). SDI showed a weak relationship with tumour stage at diagnosis and with survival: out of the seven sites s tudied, only in breast cancer was tumour extension at diagnosis signif icantly influenced by duration of symptoms, and only lung and rectal c ancers showed a detectable form of the risk function of SDI upon survi val; neither was linear, and for rectal cancer the relationship was co mplexly related with tumour stage. Hence, results show that forms of t he risk function of duration of symptoms on cancer survival are specif ic to tumour sites, and that the interval should not be represented as a linear, continuous term. Studies analysing more complex sets of fac tors, processes and forms of the SDI function are needed.