Gastrointestinal System Cancers

Esophageal cancer is the fourth most common gastrointestinal cancer and constitutes 5% of all cancers. It is common in patients older than 60 years and in black populations. The esophagus is a muscular tube that starts at the sixth cervical vertebra after the hypopharynx and extends into the stomach at the T11 level. Esophagus has an adventitial layer without serosal layer that reduces the resistance against local cancer spread. Esophageal tumors spread locoregionally through its extensive submucosal lymphatics, and distant spread is via hematogenous routes. 95% of all esophagus tumors are squamous cell cancers, 3–5% are adenocarcinomas, and others are small-cell cancer, melanoma, adenoid cystic cancer, pseudosarcoma, lymphoma, and metastatic tumors. Gastric cancer is the third most common cancer in the world and the second highest cause of cancer-related mortality. Its incidence is high in Japan, China, and Russia and is less commonly seen in the USA and Canada. Low socioeconomic status, cigarette smoking, and high alcohol consumption are correlated with gastric cancer. The stomach is an intraperitoneal organ that starts at the T11 vertebra and ends in the duodenum on the right side of the midline. Lauren classification using microscopic morphology is widely used to describe intestinal and diffuse histologic types of gastric adenocarcinoma. Gastric cancer spread patterns include local extension to adjacent organs, lymphatic metastasis, peritoneal spread, and hematogenous liver, lung, and bone metastases. The most important prognostic factor for gastric cancer is the TNM stage. The depth of primary tumor involvement, number of involved regional nodes, and distant metastasis status determine the stage. Pancreatic cancer is the second most common GIS cancer and fourth leading cause of cancer-related death in men and women in the USA. It has a high incidence in developed countries. There is racial predilection for African Americans than Caucasians with similar incidence among males and females. Pancreas cancer peak incidence is in the sixth and seventh decades. Differential diagnosis of a pancreatic mass comprises cystic adenomas, exocrine cancer, papillary cystic neoplasms, acinar cell carcinoma, lymphoma, and metastatic cancer, approximately half of which present with distant metastasis. Basic concepts that are crucial to understanding pancreatic cancer are reviewed in depth in this chapter. Colorectal cancer is the fourth most common gastrointestinal malignant neoplasm worldwide accounting for approximately 10% of all cancers with estimated 800,000 new cases a year and the second most common cause of cancer-related mortality. Rectal cancer comprises one-third of colorectal cancers, and most of the colorectal cancers (>90%) are adenocarcinomas. Colorectal cancer etiology is multifactorial comprising both environmental and genetic factors. Chromosomal instability (CIN), microsatellite instability (MSI), and CpG island methylator phenotype (CIMP) are the likely pathways leading to colorectal cancer. 5q21 mutation carrier familial adenomatous polyposis patients with autosomal dominant inheritance have 100% risk of developing colorectal cancer. The rectum is a part of the large intestine and starts at S3 and 15 cm long. The serosa is the outermost layer of the rectum, and there is no adventitia in the rectum unlike the esophagus. Anal canal cancers constitute 1% of all colorectal cancers and 10% of all rectal cancers. They are usually observed in those aged 60–65 years. Incidence is 1/100,000 in females and 0.5–0.8/100,000 in males. Anal cancer incidence is higher in urban populations than in rural populations due to implicated factors of changes in sexual behaviors, increased and persisted HPV infection in the anal canal, and increased HIV infection prevalence. The rectum forms the anal canal, which is 3–4 cm in length and ends at the anus. The anal canal is defined as either the surgical or the anatomical canal. C-myc oncogene overexpression has been implicated in the pathogenesis of anal canal squamous cell cancer and other malignancies. Most anal canal cancers are squamous cell cancers (~60%), followed by transitional cell cancers (~25%) and adenocancers (~7%). Less frequent ones are basaloid cell cancers (cloacogenic cancers) and malignant melanomas. Basic concepts that are crucial to understanding esophageal, gastric, pancreatic, rectal, and anal cancers are reviewed in depth in this chapter.

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