Incidence and current trends of colorectal malignancies in an unscreened, low risk Pakistan population

Karachi falls into a low risk region for colorectal cancer (CRC). The incidence rate is known but detailed epidemiology and pathology data regarding the disease are not available. The aim of this study was to describe CRC with reference to incidence, gender, topographic sub-site, tumor morphology, grade and stage at diagnosis and to determine the trends of incidence.

Four hundred and seventy three cases of colorectal cancer submitted to the Karachi Cancer Registry for Karachi South, years 1995-2002 were reviewed. Cases were analyzed in two time periods (1995-7 and 1998-2002) to facilitate the study of time trends.

A total of 151 CRC cases were registered during period one [86 (57%) males; 65 (43%) females] and 322 cases [210 (65%) males; 112 (35%) females] in period two. Age standardized rate (ASR) world per 100,000, crude incidence rate (CIR) and relative frequency in period one were 5.3, 3.2 and 4.1% in males and 5.5, 3.2 and 3.2% in females respectively. Corresponding figures for period two were 7.1, 4.5 and 4.7% for males and 5.2, 2.8 and 2.7% in females. The male, female ratio was equal for colon (1:1). Men had more rectal cancers (2:1) and overall CRC (1.7:1). The mean age of the patients varied with sub-site and gender from 43.7 years to 51.2 years. Cancers of the rectum presented at a relatively earlier age. Less then 5% of the cases were diagnosed in adolescents, 50% above 50 years of age and only 30% above 60 years. The ratio under-40 to above-40 for CRC patients was 0.3, which is much higher than the international average, indicating a younger age group at risk. The first cases were observed in adolescents (15-19 years) and a peak was observed in the seventh decade. Colon to rectum ratio was 1:1 in males and 2:1 in females. Most cases presented with advanced disease, though some down staging was observed in period 2 (1998-2002).

The current low but increasing incidence (especially in men), the younger age and advanced stage of CRC at diagnosis reflects a low risk, unscreened population. With existing prevalence of high risk factors in Pakistan, the low CRC incidence may be an artifact. There are concerns that an aging population over the next decade and changing lifestyle patterns may translate into a higher CRC incidence. Screening must be considered as part of the health sector planning for the future and include the high risk younger age groups.