Immunohistochemical Evaluation of Colorectal Malignancies – A Study of 100 Cases.

Colorectal Cancer Is The Third Most Common Cancer Worldwide, With An Estimated 130,000 New Patients Diagnosed Each Year. It Is The Second Leading Cause Of Death Because Of Cancer (Approximately 55,000 People Annually)[1]. In India The Incidence Of Colorectal Cancer Is 3.9 Per One Lakh Population And The Mortality Rate Is 2.8 Per One Lakh Population[2]. About 60% Of All Patients Diagnosed With Colorectal Carcinoma Will Present With Locally Advanced Disease[3]. Appropriate Therapeutic Decision Making For These Individuals Depends Primarily On The Depth Of Penetration Of The Primary Tumor And Metastatic Disease In The Regional Lymph Nodes[3]. NORMAL LARGE BOWEL The Large Bowel Comprises The Terminal 1 To 1.5 Meters Of The Gastrointestinal Tract And Is Divided Into Caecum, Ascending Colon, Transverse Colon, Descending Colon, Sigmoid Colon & Rectum. HISTOLOGY The Large Bowel Wall Is Composed Of Four Layers 1. Mucosa Epithelium Lamina Propria Muscularis Mucosa 2. Sub Mucosa 3. Muscularis Propria 4. Serosa The Mucosa Is Lined By Columnar Epithelium Into Which The Crypts Open. The Surface Epithelium Is Composed Of Absorptive Cells And Goblet Cells. In Addition The Surface Epithelium Contains Immature And Undifferentiated Cells, Endocrine Cells And Paneth Cells. The Epithelium Overlying The Lymphoid Follicles Of Lamina Propria Contains Follicle Associated Epithelial Cells Or ‘M’ Cells (M For Microfold Or Membrane Cells). The Absorptive Cells Have Basally Located Nuclei, Mucin Negative Acidophilic Cytoplasm And Luminally Directed Apical Striated Borders. They Absorb Excess Water And Electrolytes From The Intestinal Contents. The Goblet Cells Synthesize, Store And Secrete Mucin Granules. The Paneth Cells Are Seen Only In Caecum And Proximal Right Colon And They Secrete Lysozyme And Epidermal Growth Factor. Lymphocytes And Occasional Eosinophils May Be Present Between The Surface Epithelial Cells. The Crypts Are Tubular And Are Arranged Parallel To Each Other. The Lamina Propria Contains Few Lymphocytes (Both T And B Cells), Plasma Cells, Histiocytes And Mast Cells Scattered In A Network Of Collagen Fibers, Smooth Muscle Bundles, Vessels And Nerves. Lymphoglandular Complexes Are Normal Structures Formed By Deep Crypt Epithelium Surrounded By Lymphoid Follicles Which Extend From Mucosa To Submucosa. Pericryptal Fibroblast Sheath Is A Collection Of Fibroblasts And Myofibroblasts Located Around The Crypts In Superficial Lamina Propria. The Muscularis Mucosa Is Composed Of Thin Layer Of Smooth Muscles. The Submucosa Is Composed Of Loose Connective Tissue Similar To That Of Lamina Propria. It Also Contains Submucosal Plexus Of Meissner And Often Contains Fat Cells. The Muscularis Propria Is Composed Of Inner Circular And Outer Longitudinal Layers Of Smooth Muscles With The Myenteric Plexus Of Auerbach Between Them. The Outer Layer Is Collected To Form Three Thick Bands Known As Taenia Coli. The Taenia Is Shorter In Length Than The Other Layers Of The Colonic Wall. This Results In The Production Of Sacculations Or Haustrations On The Wall Of The Colon. The Serosa Is Composed Of A Single Layer Of Flattened To Cuboidal Mesothelial Cells And The Subjacent Fibroelastic Tissue. It Forms Small Pouches Filled With Fat Known As Appendices Epiploicae. The Serosa Is Missing Over The Posterior Aspect Of Ascending And Descending Colon. THE VERMIFORM APPENDIX The Appendix Is The Narrowest Part Of The Gut. The Crypts Are Poorly Formed. The Longitudinal Muscle Coat Is Complete And Thick All Around. Taenia Coli Are Absent. The Submucosa Contains Abundant Lymphoid Tissue That May Completely Fill It. The Lymphoid Tissue Is Not Present At Birth, It Gradually Increases And It Is Best Seen In Children Above 10 Years Of Age. Subsequently There Is Progressive Reduction In Quantity Of Lymphoid Tissue. THE RECTUM The Rectum Has A Continuous Coat Of Longitudinal Muscle And There Is No Taenia Coli. The Peritoneum Covers The Front And Sides Of The Upper One-Third And Only The Front Of The Middle Third. The Rest Of The Rectum Is Devoid Of A Serous Covering. WHO CLASSIFICATION OF PRIMARY TUMOURS OF COLON AND RECTUM [4] Tumours Of The Colorectal Region Are Classified Pathologically Into Different Types Which Are Based On The Microscopic Features. Epithelial Tumours Non-Epithelial Tumours I. Adenoma A. Tubular B. Villous C. Tubulovillous D. Serrated II. Intraepithelial Neoplasia A. Low Grade B. High Grade III. Carcinoma A. Adenocarcinoma B. Mucinous Carcinoma I. Lipoma II. Leiomyoma III. Gastrointestinal Stromal Tumour IV. Leiomyosarcoma V. Angiosarcoma VI. Kaposi Sarcoma VII. Malignant Melanoma VIII. Malignant Lymphoma IX. Marginal Zone Lymphoma X. Mantle Cell Lymphoma XI. Diffuse Large B Cell Lymphoma XII. Burkitt Lymphoma C. Signet Ring Cell Carcinoma D. Small Cell Carcinoma E. Squamous Cell Carcinoma F. Adenosquamous Carcinoma G. Medullary Carcinoma H. Undifferentiated Carcinoma IV. Carcinoid A. Enterochromaffin Cell B. L Cell C. Others V. Mixed Carcinoid - Adenocarcinoma ADENOCARCINOMA Adenocarcinoma Is The Most Common Tumour Type. Most Are Well To Moderately Differentiated And Lack Specific Histological Features, Although Colorectal Tumours Tend To Show Cribriform Patterns With Central Necrosis, A Feature That Is Useful If A Metastatic Tumour Is Encountered With An Occult Colorectal Primary. Dysplasia In Adjacent Mucosa May Be Seen, But Frequently The Invasive Tumour Obliterates Any Pre-Existing Polyp From Which It May Have Arisen[5]. MUCINOUS ADENOCARCINOMA This Is One Of The Subtypes Of Adenocarcinoma That Secretes Extracellular Mucin. At Least 50% Of The Tumour Must Be Mucinous In Order To Make This Diagnosis. Mucinous Adenocarcinomas Are Associated With Microsatellite Instability. Whether Mucinous Tumours Have A Better Prognosis Is Uncertain. Mucinous Change May Also Be Seen In Conventional Adenocarcinomas Treated With Neoadjuvant Chemoradiotherapy[6]. SIGNET RING CELL CARCINOMA Signet Ring Cell Carcinoma Is Composed Of At Least 50% Cells With Intracytoplasmic Mucin And Eccentrically Placed Nuclei, Resembling Gastric Signet Ring Cell Tumours. The Tumour Grows In A Diffuse Fashion[7]. SMALL CELL CARCINOMA Small Cell Carcinoma May Have Areas Of Glandular Or Squamous Differentiation. The Prognosis Is Extremely Poor[8]. SQUAMOUS AND ADENOSQUAMOUS CARCINOMAS These Are Extremely Rare Tumours. They Have Been Associated With Ulcerative Colitis, Schistosomiasis And Pelvic Irradiation. The Survival Rates Are Similar To Adenocarcinomas. The Following Criteria Is Essential For Making The Diagnosis Of Squamous Or Adenosquamous Carcinomas § There Must Be No Other Sites Of Squamous Cell Carcinoma In The Body § There Must Be No Involvement Of Cloacogenic Or Squamous Lined Mucosa[9]. MEDULLARY CARCINOMA This Is An Important Subtype Of Colorectal Cancer, Added To The WHO Classification In 2000. It Has A Characteristic Phenotype With Sheets Of Cells And Numerous Tumour Infiltrating Lymphocytes On Microscopy. This Phenotype Is Associated With The Lynch Cancer Family Syndrome (Hereditary Non-Polyposis Colorectal Cancer). Patients With This Syndrome May Also Have Ovarian, Endometrial, Skin And Other Gastrointestinal Tumours. The Colorectal Tumours Show A Loss Of Mismatch Repair Proteins Such As MSH (Muts, Escherichia Coli, Homolog In 60% Of Cases) Or MLH (Mutl, Escherichia Coli, Homolog In 30% Of Cases), Which Can Be Demonstrated With Immunohistochemistry[10]. UNDIFFERENTIATED CARCINOMA They Represent Less Than 1% Of Colorectal Cancers. They Are Malignant Epithelial Tumours That Have No Glandular Or Other Features To Indicate Definite Differentiation. The Absence Of Intracytoplasmic Mucin Helps To Differentiate These Tumours From Poorly Differentiated Adenocarcinomas[11]. CARCINOIDS AND NEUROENDOCRINE CARCINOMA They Are Rare In The Colon But Focal Neuroendocrine Differentiation Can Occur In Conventional Adenocarcinomas. These Are Commonly Seen In Caecum And Rectum[12]. MIXED CARCINOID - ADENOCARCINOMA They Originate From The Endodermally Derived Multipotential Cells Located At The Base Of The Crypts Which During The Neoplastic Transformation Undergo Differentiation Along Several Different Pathways[13]. MESENCHYMAL TUMOURS Mesenchymal Tumors In The Colorectum Are Rare. Histologically They Resemble Their Counterparts In Soft Tissues. Leiomyoma Is The Commonest Mesenchymal Tumour[14]. LYMPHOMA Lymphomas Are Less Frequent In Large Bowel. They Are Nearly Always Of Non- Hodgkin’s Type. Most Of Them Belong To MALT-Type (Mucosa Associated Lymphoid Tissue) Category[15]. METASTATIC TUMOURS Metastases Form Disc Like Areas With Central Ulceration. They Originate From Malignant Melanoma, Lung Tumours, Renal Cell Carcinoma Or Mesothelioma.[16] Colorectal Adenocarcinomas Affect Males Slightly More Than Females And The Mean Age Of Incidence Is 62 Years. Both Environmental And Genetic Factors Are Involved In The Cause And Pathogenesis. There Are A Number Of Genetic Mutations Involved In Colorectal Carcinogenesis. These Can Be Assessed By Immunohistochemistry. Mutations In P53 Have Been Found To Occur In 70% To 80% Of Patients With Colon Cancer[1]. This P53 Mutation Was Proposed As A Late Event In The Transition From Adenoma To Carcinoma. Preclinical Investigations Have Demonstrated That Mutant P53 Renders Malignant Cells Less Sensitive To Most Chemotherapeutic Agents, With The Exception Of The Taxanes, Which Seem To Be Indifferent To P53 Status. The Purpose Of This Study Is To Analyse The Age, Sex And Site Distribution In Colorectal Adenocarcinomas In Our Institution And To Investigate The Level Of Expression Of P53 In Colorectal Adenocarcinomas And Correlate This With The Histological Grade And Stage