cáncer colorrectal

Cáncer Colorrectal: Introducción y Estadísticas

Presentación del Dr. Jorge Zapata

• El Dr. Jorge Zapata inicia la clase sobre cáncer colorrectal, destacando su prevalencia en países desarrollados como Norteamérica y Australia.

Importancia del Cáncer Colorrectal

• Este tipo de cáncer es uno de los más comunes en el tubo digestivo y se puede prevenir; se celebra el Día Mundial de la Lucha contra el Cáncer de Colon el 31 de marzo.

Anatomía del Colon

• El colon, que mide aproximadamente entre 1.40 a 1.60 metros, incluye varias partes: ciego, colon ascendente, transverso, descendente, sigmoides y recto (15 cm finales). Su función principal es actuar como reservorio final y absorber agua y electrolitos.

Irrigación y Drenaje Venoso

• La irrigación del colon proviene de las arterias mesentéricas superior e inferior; el drenaje venoso se realiza a través de las venas mesentéricas que forman la vena porta para detoxificación hepática.

Estadísticas Globales y Locales sobre Cáncer Colorrectal

Incidencia Mundial

• A nivel mundial, el cáncer colorrectal es la tercera causa más importante de cáncer y la segunda causa de muerte; en Perú ocupa la cuarta posición tanto en incidencia como en mortalidad.

Factores de Riesgo

• Los factores incluyen sobrepeso, antecedentes familiares, consumo de tabaco/alcohol, vida sedentaria y dieta rica en carnes rojas o ahumadas; algunos son modificables mientras que otros no lo son (como la edad).

Mecanismos Genéticos del Cáncer Colorrectal

Mutaciones Genéticas

• La aparición del cáncer implica una serie de mutaciones genéticas que afectan genes reparadores del ADN, estimulan prooncogenes e inhiben genes supresores tumorales; estas mutaciones pueden tardar años o incluso décadas en manifestarse como tumores.

Vías Carcinogénicas

• Existen tres vías principales para el desarrollo del cáncer colorrectal:

• Vía Supresora: Representa el 85% de los casos esporádicos.

• Vía Mutadora: Asociada al 15% restante.

• Ambas vías implican alteraciones genéticas significativas que predisponen a tumores malignos.

Lesiones Precursoras y Tipos Histológicos

Lesiones Precoces

• Las lesiones precoces incluyen adenomas o pólipos adenomatosos que son premalignos; estos pueden evolucionar hacia adenocarcinomas si no se detectan a tiempo.

Understanding Colon Cancer Development

Early Stages of Colon Cancer

• The normal colon epithelium can develop into an adenoma or polyp, which is a growth of cells towards the lumen. This early polyp is small and begins to accumulate genetic mutations.

• The first significant mutation occurs in the APC gene, marking one of the initial steps in cancer progression. As the polyp matures and grows, additional mutations arise, including a critical mutation in the TP53 gene.

• The presence of these mutations indicates a transition from benign adenoma to potential malignancy, with advanced adenomas showing signs of carcinoma development.

Progression to Invasive Cancer

• Most colon cancers (98%) are adenocarcinomas; other types like lymphomas and sarcomas are rare. The left side of the colon is more frequently affected by cancer.

• Polyps initially form on the mucosal surface but can invade deeper layers over time, leading to metastasis through lymphatic and hematogenous routes.

Metastasis Patterns

• Lymphatic spread is typically the first route for metastasis, affecting nearby lymph nodes. Hematogenous spread follows, primarily targeting the liver due to its venous drainage system.

• The lungs are also common sites for metastatic spread after liver involvement.

Risk Factors for Colon Cancer

• Age significantly influences risk; incidence peaks between 60 and 65 years old. A notable increase in risk starts at age 45 or 50.

• Environmental factors such as alcohol consumption, tobacco use, high-fat diets, chronic inflammatory diseases (like IBD), and family history contribute to increased risk.

Genetic Predispositions

• General population risk for developing colon cancer is about 6%. Family history amplifies this risk significantly—especially with multiple relatives having polyps or colorectal cancer.

• Conditions like familial adenomatous polyposis lead to nearly universal development of colorectal cancer if not monitored closely from adolescence onward.

Chronic Inflammatory Diseases Impact

• Long-standing ulcerative colitis increases colon cancer risk by 1% each year after ten years. Crohn's disease raises this risk up to twentyfold due to associated inflammation and polyp formation.

• Images illustrate various stages of polyp development alongside invasive tumors within surgical specimens.

This structured overview provides insights into how colon cancer develops from benign lesions through genetic mutations while highlighting key risks associated with its progression.

Understanding Polyps and Their Risks

Types of Polyps

• There are two main types of polyps: inflammatory (non-neoplastic) and adenomatous (neoplastic). The most common type is hyperplastic or inflammatory, which has a negligible cancer risk.

• Adenomas, accounting for about 8% of all polyps, are considered dangerous. They include three subtypes: tubular, tubulovillous, and villous adenomas. Villous adenomas carry the highest cancer risk.

Risk Factors for Cancer Development

• The size of the polyp is a significant risk factor; polyps larger than 10 mm have a higher likelihood of containing adenocarcinoma. Smaller polyps rarely contain cancer.

• Other risk factors include obesity, sedentary lifestyle, and diets high in fat and processed meats.

Screening Guidelines

• Current guidelines recommend that asymptomatic individuals begin screening for colon cancer at age 45 with a colonoscopy. Symptomatic patients may require earlier screening based on individual assessment.

• If colonoscopy is unavailable, fecal occult blood tests should be performed; positive results necessitate referral for colonoscopy.

Prevention Strategies

• Preventive measures include dietary changes such as increased fiber intake and reduced consumption of saturated fats, processed meats, and red meats.

Clinical Presentation

• Early-stage lesions often present no symptoms or only vague discomfort like flatulence or minor bowel habit changes. Advanced lesions can lead to more specific symptoms depending on their location in the colon.

Symptoms and Diagnosis

Symptoms Based on Tumor Location

• Right-sided tumors may cause anemia due to bleeding; left-sided tumors typically result in constipation or intestinal obstruction due to their stenosing nature.

Diagnostic Indicators

• Initial diagnosis relies on clinical presentation; symptoms may include abdominal pain, weight loss, altered bowel habits (constipation/diarrhea), signs of lower gastrointestinal bleeding (melena/hematochezia), or anemia.

Diagnostic Procedures

Essential Diagnostic Tools

• Colonoscopy with biopsy is the gold standard for diagnosing suspected colorectal cancer. CT scans can assist in staging but are not primary diagnostic tools.

Staging Process

• After diagnosis via colonoscopy, staging involves imaging studies like contrast-enhanced CT scans to assess tumor spread. Tumor markers support diagnosis but primarily aid post-treatment monitoring.

Staging Classifications

Classification Systems

• Various classifications exist for staging colorectal cancer:

• Dukes Classification: Ranges from A (mucosal lesion only) to D (distant organ involvement).

• TNM Classification: Evaluates tumor size/invasion depth (T), lymph node involvement (N), and metastasis presence (M).

Cancer Staging and Treatment Overview

Understanding Cancer Staging

• The TNM staging system is used to classify cancer based on tumor size (T), lymph node involvement (N), and metastasis (M).

• Early-stage cancers (Stage 0) have a 100% survival rate, while advanced stages with distant metastasis show significantly lower survival rates, often under five years.

Surgical Treatment Approaches

• Surgical intervention is the primary treatment for locally advanced colon cancer without distant metastasis. Stage 0 involves removing polyps with carcinoma foci, ensuring complete resection.

• For locally advanced cancers without lymph node or organ metastasis, surgeries like hemicolectomies are performed based on the tumor's location.

Hemicolectomy Techniques

• Hemicolectomies are categorized as right or left based on the tumor's position in the colon. Segmental resections are less common now due to advancements in surgical techniques.

• Current practices favor extensive resections over segmental ones for locally advanced lesions to ensure comprehensive removal of cancerous tissue.

Rectal Cancer Considerations

• Rectal cancer presents unique challenges due to its proximity to critical structures; achieving clear margins during surgery is more complex compared to colon cancer.

• Rectal tumors can be radiosensitive, allowing pre-surgical radiation therapy to shrink tumors before surgical intervention.

Diagnostic Imaging for Rectal Cancer

• Accurate staging of rectal cancer requires both CT scans and pelvic MRIs; MRI is superior for assessing pelvic tumors.

• Initial stages of rectal cancer may allow for direct surgical intervention, but more advanced cases necessitate a combination of neoadjuvant therapy followed by surgery and adjuvant chemotherapy.

Surgical Options in Advanced Rectal Cancer

• In cases where rectal tumors invade surrounding tissues, preserving sphincter function becomes crucial; various surgical approaches exist depending on tumor size and location.

• If necessary, extensive resections may lead to colostomy; however, efforts are made to minimize such outcomes through careful planning and execution of surgeries.

Cáncer de Colon: Diagnóstico y Prevención

Importancia del Cáncer de Colon

• El cáncer de colon es la segunda causa de muerte a nivel mundial y la cuarta en Perú, destacando su relevancia como uno de los cánceres más significativos.

• El 98% de los casos son adenocarcinomas, siendo los pólipos adenomatosos vellosos las lesiones precoces con mayor riesgo de malignidad.

Diagnóstico y Prevención

• La colonoscopía es el estándar para el diagnóstico, permitiendo la evaluación completa del colon y la identificación activa de pólipos durante el procedimiento.

• Se recomienda que todas las personas a partir de los 45 años se realicen una colonoscopía para descartar adenomas o cáncer, incluso si no presentan síntomas.

Manejo Oncológico

• En casos avanzados (grados dos y tres), se puede utilizar neoadyuvancia que incluye radioterapia o radioquimioterapia antes de la cirugía para reducir el tamaño tumoral.

• La reducción del tumor permite realizar una resección quirúrgica respetando márgenes adecuados, lo cual es crucial para un tratamiento efectivo.

Procedimientos Quirúrgicos

• Si se detectan pólipos grandes (más de 10 mm), estos pueden requerir planificación para polipectomía en lugar de extirpación inmediata durante la colonoscopía.

• Lesiones más pequeñas o sin invasión submucosa pueden ser tratadas mediante técnicas endoscópicas curativas, logrando tasas de sobrevida a cinco años del 100%.

Conciencia y Educación

• Es fundamental promover la realización regular de colonoscopías entre familiares mayores de 45 años para prevenir complicaciones graves asociadas al cáncer colorrectal.