Anal cancer overview

# Overview
Anal cancer is a type of cancer which arises from the anus, the distal orifice of the gastrointestinal tract. It is a distinct entity from the more common colorectal cancer. The etiology, risk factors, clinical progression, staging, and treatment are all different. Anal cancer is typically a squamous cell carcinoma that arises near the squamocolumnar junction and its often linked to human papillomavirus (HPV) infection. It may be keratinizing (basaloid) or non-keratinizing (cloacogenic). Other types of anal cancer are adenocarcinoma, lymphoma, sarcoma or melanoma. Treatment depends on the stage of the disease at the time of diagnosis.

# Classification
Anal cancer may be classified according to histology into four subtypes: squamous cell carcinoma, adenocarcinoma, lymphoma, and sarcoma.

# Pathophysiology
Anal cancer most commonly arises from squamous cells at the squamocolumnar junction. Other types of anal cancer are adenocarcinoma, lymphoma, and sarcoma.

# Epidemiology and Demographics
In 2008-2012, the incidence of anal cancer was estimated to be 1.8 cases per 100,000 individuals in the US.

# Risk Factor
The most potent risk factor in the development of anal cancer is Human Papillomavirus (HPV). Other risk factors include receptive anal intercourse with multiple sexual partners, smoking, and immunosuppression.

# Screening
Screening for anal cancer by pap smear is suggested among HIV-positive patients and homosexual men.

# Causes
Squamous carcinoma of the anus may be caused by HPV infection.

# Differential Diagnosis
Anal cancer must be differentiated from other diseases that cause anal pain, anal pressure, and hematochezia, such as, anal fissure, and neoplastic ulcers.

# Natural History, Complication, and Prognosis
Depending on the extent of the tumor at the time of diagnosis, the prognosis may vary. The three major prognostic factors are site (anal canal vs. perianal skin), size (primary tumors <2 cm in size have better prognoses), and lymph nodes involvement.

# Staging
The staging of Anal cancer is based on the TNM staging system 

# History and Symptoms
Symptoms of anal cancer include pain or pressure in the anus or rectum, anal itching and anal discharge.

# Physical Examination
Common physical examination findings of anal cancer include a lump near the anus and rectal bleeding.

# Diagnostic Studies
Laboratory Studies
There are no diagnostic lab findings associated with anal cancer.
MRI
Pelvic MRI may be diagnostic of anal cancer.
CT
CT may be helpful in the diagnosis and staging of anal cancer.
Ultrasound
Endoanal ultrasound may be helpful in the diagnosis, staging, determination of the depth of penetration, and to monitor the response to chemo and/or radiation therapy to anal cancer.
Other Imaging Studies
PET-CT may be helpful in anal cancer staging.
Other Diagnostic Imaging
Anoscopy, proctoscopy, and biopsy maybe helpful in the diagnosis of anal cancer.

# Medical Therapy
The predominant therapy for anal cancer is chemotherapy and radiation.

# Surgery
Surgical resection is not recommended among patients with advanced or metastatic anal cancer.

# Primary Prevention
HPV vaccine is recommended for homosexual men, bisexual men, and women who engage in receptive anal sex to prevent anal cancer. Other primary prevention strategies include smoking cessation and condom use.