INTRODUCTION
It is difficult to determine the exact incidence of non-melanoma skin cancers (NMSCs) in Africa because most cases are unreported. This is partly due to inadequate cancer registry in most of the hospitals in Africa. Studies have shown that there is an increase in the incidence of NMSCs worldwide roughly by 3-8% per year.[1] Australia and New Zealand have the highest incidence of NMSCs in the world.[12] NMSCs include squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Studies have shown that SCC is more common in Blacks while BCC is commoner in Caucasians.[23] BCC accounts for 75% of NMSC cases and is the most common skin cancer in Caucasians.[3] Reports from Nigeria and other parts of Africa show that SCC due to chronic ulcer is the most common risk factor of skin malignancy.[456]
Ultraviolet (UV) radiation on generalized hypopigmented skin remains the major risk factor for NMSCs in Caucasians, whereas in Blacks, chronic ulcers, chronic inflammatory lesions such as chronic osteomyelitis, and old scars have been implicated as the major risk factors of NMSCs.[7] SCC may slowly evolve through the precursor lesions like actinic keratosis, severe squamous cell dysplasia and carcinoma in situ.[8] UV radiation, a potent carcinogen, is usually filtered out by the ozone layer. Therefore, ozone layer depletion should be a source of concern to the oncologist and public health personnel.[9]
Therefore, this study was aimed at defining the frequency and morphological patterns of NMSCs in University of Benin Teaching Hospital (UBTH), Benin City, Nigeria. It is hoped that data derived from this research will be useful in the management of these lesions and as well serve as baseline data for further research.
MATERIALS AND METHODS
Study setting and design
Data of surgical biopsies of skin tumor received at the Department of Histopathology, UBTH over a 26-year period (from January 1982 to December 2007) were scrutinized for this study. These specimens were sent by the departments of dermatology and surgery in UBTH and other hospitals within Benin City metropolis as well as in the neighboring southern states of Nigeria. The original pathology request cards of the cases were retrieved to obtain socio-demographic data on age, sex, hospital numbers, and clinical information .
Specimen sampling and laboratory procedure
All specimens sent for histology were fixed in 10% formalin solution, processed with Histokinette automated tissue processor, paraffin embedded, and sectioned into 3 to 5 μm thin slices using the microtome machine, before they were stained with hematoxylin and eosin. The results obtained were analyzed with respect to age, sex, and tumor type. Special stains including reticulin and Periodic Acid Schiff stains were used where necessary.
Exclusion criteria
Patients with metastatic malignancies, incomplete demographic data, or unverifiable histological diagnosis were excluded from the study.
Data management
Data obtained were analyzed using the SPSS version 17 statistical package.
RESULTS
Demographic analysis
During the 26-year period (1982-2007) of this study, there were 187 cases of malignant skin cancers. Of these, 63 cases accounting for 33.7% were NMSCs. SCC accounted for 45 cases, constituting 24.1% and 71.4% of all malignant skin tumors and NMSCs, respectively. BCC accounted for 18 cases, constituting 9.6% and 28.6% of all malignant skin tumors and NMSCs, respectively. The peak incidence of SCC and BCC was in the 5 th decade of life. The age range for SCC and BCC was 26-74 and 23-71 years, respectively. The mean ages for SCC and BCC were 51.4 ± 1.3 and 46.3 ± 5.2 years, respectively [Table 1].
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Table 1: Age and sex distribution of non-melanocytic skin cancer
This study confirmed the male to female ratio of SCC and BCC to be 2.4:1 and 1.6:1 respectively. Table 2 illustrates the site distribution of non-melanoma skin cancer. SCC and BCC occurred most commonly in the head and neck region. Of the 42 cases of SCC with recorded site distribution, in 20 cases (47.6%) the head and neck region, in 14 (33.3%) cases the leg and foot, and in 4 cases (9.5%) each, the trunk and forearm/hand region were affected. The anogenital region was not affected in any of the cases. Of the 18 BCC cases, 13 were albinos while 5 were dark-skinned patients. Of the 16 BCC cases with recorded site distribution, in 12 cases (75%) it occurred in the head and neck and in 4 cases (25%) in the trunk region.
Table 2: Site distribution for 58 non-melanoma skin cancer
Histopathologic analysis
Table 3 shows the grades of SCC. Of the 45 cases of SCC, 24 cases (53%) were large keratinizing SCC (well differentiated). Other grades of SCC in this study were large non-keratinizing SCC (n = 10, 22.2%) and small non-keratinizing SCC (n = 3, 6.7%). The other very rare variants are presented in Table 3. The common BCC accounted for 50.0% of all BCC variants in this study. Keratotic BCC accounted for 6 cases (33.3%) and was the second most common BCC recorded. Sclerosing morphea-type BCC accounted for 2 cases (11.1%). Superficial BCC accounted for 1 case (5.6%) as seen in Table 4.
Table 3: Histological types of squamous cell carcinoma
Table 4: Histological types of basal cell carcinoma
DISCUSSION
Our study in UBTH, Benin City has shown that NMSCs constituted 33.7% of all skin cancers in this center. This is slightly at variance with the studies done in the United States of America, where NMSC is of higher incidence, accounting for 40% of all skin malignancies, with greater than 1.2 million new cases diagnosed yearly.[10] However, Australia has the utmost incidence of NMSCs globally, with about 1000/100,000 cases reported annually. The reason for this variation is partly attributable to geo-ethnical variation in the distribution of skin cancer and the fact that most cases in Africa are underreported.
SCC was the most common NMSC in this study, constituting 71.4%. This is similar to other studies done in Nigeria and on African albinos and Black Americans where SCC was the most common NMSC, as compared to their Caucasian counterparts.[1112] The mean age of patients with SCC was 51.4 ± 1.3 years in this study. This report is markedly different from the findings recorded in Singapore where its mean age was reported as 83.9 years.[13] No definitive reason could be attributed to the marked variation in both mean ages.
The head and neck was the most common site for SCC in our study. This report is, however, similar to the findings from Singapore, United States of America, and globally.[131415] It is expected that since sun exposure is the major predisposing factor, chronic UV radiation causes damage to fair-skinned Caucasians and albinos with poor tanning ability.[14] In majority of Caucasians, SCC arises in specific areas such as the forehead, face, neck, ears, and scalp, which are directly exposed to the sun. However, some unexposed sites including buttocks, genitalia, and legs are occasionally effected.[1516]
In the Negroid population, predisposing factors for skin cancer include Marjolin's ulcer, chronic ulceration, trauma, burns, chemical carcinogens, albinism, immune suppression; discoid lupus erythematosus, and xeroderma pigmentosum.[17] SCC is found more commonly in the elderly and less commonly in young individuals. Studies have shown that SCC normally follows an indolent course. This may be the reason why most African patients may not find it necessary to report to health facilities for proper assessment and follow-up. In addition, most of the patients with indolent ulcers are illiterate and lack resources for medical care evaluation.
In this study, different histological variants of SCC were encountered. However, among these, large keratinizing SCC was the most commonly encountered variant of SCC in this study. This is similar to reports from other parts of Africa and on Blacks in America.[1112]
In our study, BCC accounted for only 9.6%. This is in contrast to Caucasian studies where BCC is reported as the most common NMSC, accounting for 70-80%.[1118] However the value obtained in this study is slightly higher than the 2%, 2%, 3.9% and 4% reported from Zaria, Maiduguri, Jos, and Kano, respectively.[4121511] The mean age of patients with BCC was 43.6 ± 5.2 years in this study. This report is at variance with the findings from the United States of America where the mean age of patients with BCC was reported as 55 years.[1819] In our study, BCC occurred predominantly in albinos, accounting for 72.2% of all BCCs. This is similar to the study of Brown et al.,[20] who reported that 75% occurred in albinos. Although it has been claimed that BCCs do not affect Black Africans, quite a number of these cases occurred in African albino patients in this study. This is due to the fact that African albinos lack melanin pigment which is a major protective device against skin cancer, as compared to Blacks with heavy melanin pigmentation.
BCC, also known as rodent ulcer, is an indolent malignant ulcer. Reports have shown that Black Nigerians do suffer from rodent ulcers.[1819] The head and neck region, especially the face, is commonly affected. Retrospective studies done in Port Harcourt reported that BCC was found in 22% patients with face lesions.[18] Though most of the BCCs are induced, environmental influence, age, gender, race, and DNA repair capacity are also the known risk factors that contribute to the development of BCCs.[18] There is a genetic association to BCC as evidenced in the rare inherited autosomal dominant basal cell nevus syndrome (BCNS) - a disorder made up of multiple BCCs and other associated disorders of nervous skeletal and reproductive systems.[18]
In this study, the most encountered variant was the common BCC accounting for 50%. This is similar to reports from Caucasian series.[1819] Sclerosing-type, sometimes called morpheic or desmoplastic type, accounted for 11% in our study. This is slightly at variance with Caucasians' report where it accounted for about 5%. The reason for this variation cannot be ascertained.
CONCLUSION
In this study, SCC was the most common NMSC. This is similar to other reports of Africans and blacks Americans. Nevertheless, in contrast to our findings, BCC is the most common NMSC in Caucasian series. Again, the head and neck region was the most common site of NMSCs. This is also similar to reports from other parts of the world.
Source of Support:
Nil
Conflict of Interest:
None.
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