Lip Cancer: A 10-Year Retrospective Epidemiological Study

Discussion

Approximately 25% of all oral tumors are carcinomas of the lip, although some reports claim a tendency of this percentage to decrease (1, 4, 8). The lip is the most prevalent site of oral cancer in some geographical areas, e.g. Australia, Canada and Spain (4, 7, 9). The major histological types of lip cancer are SCC and BCC.

The tumor, in its initial phase, usually appears as a papule or a plate which tends to progress into a vegetative or ulcerative form. In these cases, a biopsy is indispensable to confirm the diagnosis of carcinoma. Although in the case of T1 or T2 lesions, the percentage of patients with lymph node metastases at the time of diagnosis is 8%, this figure increases considerably in advanced-stage tumors, making it necessary to search for possible cervical metastatic adenopathies (2).

Different risk factors have been associated with lip tumors such as age, chronic exposure to solar radiation and tobacco and alcohol habits. Several reports suggested the pathogenic role of some viral factors, such as Human Papilloma Virus (HPV) 16 and 24 and Herpes Virus (HSV) 1 and 2, especially in immune-depressed individuals (10, 11). In particular, the association of HSV2, exposure to UV rays and chemical factors can considerably increase the risk of these tumors (8).

In our retrospective analysis of a large number of cases, we were able to characterize the two most common lip cancer types and to correlate these with age, sex, anatomical site and risks factors of solar radiation exposure and tobacco and alcohol drinking habits.

In accordance to the literature data, we found an increase in lip cancer incidence with increasing age (12). In our sample, lip carcinomas were most frequent in those aged 60-70 years, with a mean age of 65.4±13.6 years. This could be a result of accumulation of molecular changes due to exposure to factors such as tobacco and other carcinogens, or as part of the biological ageing process that has been shown to be linked to accumulation of DNA damage (13, 14).

SCC is the most frequent histological type of malignant tumor of the lip region, as shown in our sample, while BCC is uncommon in this area. Some authors doubt that this histological type is a primary lesion of the lip and suggest that it probably arises in the skin from where it subsequently infiltrates the vermillion border and labial mucosa.

Another important feature is the difference in incidence and tumor type distribution according to sex. We found a higher number of lip cancer cases among men than women, with a male to female ratio of 4.6:1. These differences might be due to occupational and behavioral differences between the sexes: a higher percentage of men working outdoors or taking part in outdoor leisure activities. Some investigators have also suggested the value of women's lipstick, a known protector against solar exposure of the lip (15). Carcinomas of the lower lip most frequently occur in male smokers working in the open air, such as sailors, fishermen and farmers. It occurs especially among Caucasians. Dark skinned people are probably protected against UV rays by their natural skin pigment (16).

In accordance to the literature data, we also found that SCC is the most frequent histological type among men, while BCC is more frequent in women.

The lower lip is the most affected anatomical site (2, 6, 17) and SCCs are the most frequent in these patients. The higher occurrence of disease of the lower lip has been attributed to its position, which usually means that it receives a higher exposure to solar radiation and is also more subjected to the action of the other factors such as tobacco and alcohol (16).

As reported in the literature data (3, 17, 18), in our study, nearly all cases of SCC occurred in the lower lip, while BCCs were generally located in the upper lip. Interestingly, this finding gives credit to many authors that suggested that the etiology of upper lip cancer could be regarded as a separate entity and different from that of the lower lip (19).

In our series, there is evidence to confirm the independent effect of exposure factors related to lip carcinoma. We found a significant association between lip cancer and risk factors such as solar radiation exposure and tobacco and alcohol drinking. Chronic exposure to solar ultraviolet radiation is the most widely accepted cause of lip cancer. UVB radiation, together with UVA, produces mutations in DNA. Tumor development is the result of failure to repair these mutations (10, 20). Exposure to UV radiation is measured by lifelong cumulative exposure to sunlight. Accumulated solar exposure during work is associated with a constant level of exposure over the years. This is consistent with the greater frequency of lip cancer in males and with previous findings concerning the prevalence of agricultural, forest and fishery professions in relation to this type of cancer. It is also coherent with the fact that lip cancer is rare on the upper lip.

As suggested above (21, 22), the occurrence of tobacco and alcohol drinking habits were significant in our sample: 72.96% of patients were smokers and 72.04% had an alcohol habit. Smoking is an important factor in lip SCC and the malignant lesion will occur in the location where the cigarette, cigar or pipe is placed (7, 23). We found a significant association between tobacco habit and SCC of the lower lip. The same finding was made for alcohol drinking habit. It is probable that tobacco and alcohol beverage products might also be associated with occurrence of the disease in the lower lip.

Some authors found an interaction between alcohol consumption and the habit of leaving the cigarette on the lip while smoking, which is independent of the cumulative amount of tobacco smoked (7). So, according to them, the effect of alcohol is more important in those with this habit.