The relative frequency of malignant disease varies with sex, age, race and geographic location. The frequency differs among the developed and developing countries. A review of the first 5000 histologically confirmed
malignancies seen at the Riyadh Armed Forces Hospital Oncology Department confirmed differences from those encountered elsewhere. With the absence of a National
Cancer Registry, only relative frequencies can be reported. In this series,
gastrointestinal tract cancers were the most frequent, at nearly 18%, with high relative frequency of
cancers of the liver and esophagus. Colorectal
malignancies were less frequent than in the West.
Lymphoma was the second most frequent
malignancy at 13% with 2.5:1 ratio of
non-Hodgkin lymphoma to
Hodgkin disease. In both groups, poor prognostic histological varieties were more frequent than in the West.
Breast cancer was the most frequent
malignancy in females, accounting for 24% of all female
cancers, in spite of the infrequency of the traditional risk factors of nulliparity, late age of first pregnancy, late age of menopause, and high
dietary fat consumption. Two-thirds of patients with
breast cancer were premenopausal. Other
malignancies encountered at a higher frequency than in developed countries include
hepatocellular carcinoma and
nasopharyngeal cancer. This high relative frequency could be related to the high incidence of viral
hepatitis and
Epstein-Barr virus infections, respectively. The high relative frequency of oral cavity
cancers is presumed to be due to chewing Qat and Shama.
Thyroid cancer relative frequency was just over 5%, with a high predominance in females. No obvious etiological factors are identified. The relative frequency of bronchogenic
cancer is low at 5%. This is likely to increase with the progressive rise in the habit of cigarette smoking.
Skin cancer, on the other hand, is low, presumably due to the traditional dress covering the entire body and the head.