Table 1.

Characteristics of the two groups of potentially malignant oral lesions analysed

	Cases	Controls
Patients' sex
Male	5	5
Female	13	13
Patients' age (years)
Mean	59.6	59.5
SD	14.3	13.5
Range	27–80	34–78
Site of lesion
Tongue	8	9
Floor of mouth	2	4
Other location within the oral cavity	8	5
Patients' smoking habits*
Ex-smoker	1	1
Non-smoker	3	4
<10 cigarettes/day	2	2
10–20 cigarettes/day	3	0
>20 cigarettes/day	9	10
Follow up time (months)
Mean	60	77
SD	31	42
Range	6–138	24–160
Field
1 site (localised lesion)	7	5
>1 site/continuous (diffuse lesion)	4	4
>1 site/independent (multifocal lesions)	7	9

Cases consisted of all potentially malignant oral lesions (PMOLs) that progressed to carcinoma for which material was available. Controls were selected from a larger group of PMOLs that did not progress to carcinoma to match the cases in number and in the parameters referred to in the table. Field refers to the number of oral sites occupied by PMOLs and the relative location. When diffuse and multifocal lesions were present in the oral mucosa of the same patient they were entered as multifocal.

*One patient from the cases was a pipe smoker and was not included in the table.