Colorectal Cancer Epidemiology and Characteristics

Introduction to Colorectal Cancer

Adenocarcinoma is the most common cancer of the large intestines, accounting for 95-98% of all colorectal malignancies 1
The American Cancer Society and other guideline societies suggest that colorectal cancer represents the third most common cancer worldwide, accounting for approximately 10% of all tumor types globally, with over 1.1 million new cases annually 2, 3, 4

Among colorectal cancers, colon cancer is more frequent than rectal cancer, with a ratio of 2:1 in high-risk populations 5, 6
Colorectal cancer is the second leading cause of cancer death worldwide, with approximately 600,000-930,000 deaths estimated each year 3, 4

Adenocarcinomas comprise 95-98% of all rectal and colonic malignancies, typically arising from adenomatous polyps through the adenoma-carcinoma sequence 1
The majority of colorectal adenocarcinomas are characterized by chromosomal instability (CIN), which represents the common pathway observed in approximately 85% of cases 1
Microsatellite instability (MSI) is rare in rectal cancer (only a few percent) but accounts for approximately 15% of all colorectal cancers, predominantly affecting the right colon 1

Approximately 15-30% of patients present with metastatic disease at diagnosis, and an additional 20-50% of patients with initially localized disease will develop metastases during their disease course 4
The World Health Organization and other health organizations note that colorectal cancer presents as an emergency in approximately 30% of cases, with large bowel obstruction representing 80% of these emergencies (15-30% of all CRC) and perforation accounting for the remaining 20% (1-10% of all CRC) 7

The Philippines exhibits a markedly higher proportion of rectal cancers (≈ 50 % of cases) and a lower colon‑to‑rectum ratio compared with Western populations, where the typical colon‑to‑rectum ratio is about 2 : 1. 8, 9

Filipino patients are diagnosed at a mean age of roughly 55 years, which is considerably younger than the median age of about 70 years reported in Western cohorts. 8

In the Philippines the male‑to‑female ratio for colorectal cancer is approximately 1:1, whereas many other Asian nations exhibit a markedly higher incidence in males, indicating a less pronounced sex disparity in the Filipino population. 10

Colorectal cancer ranks among the most common malignancies for both sexes across Asia, but the Philippines records lower incidence rates than high‑incidence Asian countries such as Japan, South Korea, Singapore, and Hong Kong. 11
Compared with Western nations, the Philippines (along with India and Vietnam) shows a noticeable gap in colorectal cancer incidence, reflecting regional differences in disease burden. 11