More diagnostic indexes from general practice for some important forms of cancer

Abstract

A method of calculating positive predictive values (PPVs) and likelihood ralios (LRs) on the basis of Bayesian probabilities has been described previously. In the present article the method is applied to a sore which does not heal in relation to skin cancer, a lump in the breast in relation to female breast cancer, genital bleeding in relation to internal genital cancer in fernales and indigestion in relation to stomach cancer. For non-healing sores or moles, PPV increased with age from 0.5-0.8% to 3.8-5.8%. LR exceeded 100 for the younger age groups. The PPV or lump in the breast for breast cancer increased steadily from 0.2- 0.3% to 4.1-6.5% up to 70 years or age. The LR was 50-79 for the age group 20-29 years but fell to around 20-40 in intermediate age groups. After the age of 70 years there was a steep rise in PPV to 30.7%-48.3% and in LR to 167-355. For genital bleeding the PPV rose from less than 1% before the menopause to 22-50% after the menopause, falling again to 7.3%-15.0% for women 70 years old or older. LR changed from around 10 before the menopause to three-figure values after. The PPV or indigestion for stomach cancer increased slightly with age from <0.1% to 2.4%. Most LR values varied in the 10-40 range, decreasing slightly with increasing age. There were no significant sex differences. The validity of the results is discussed.