Basal cell carcinoma overview

# Overview
Basal cell carcinoma is one of the most common skin cancers. It is commonly known as rodent ulcer. In 1827, Jacob Arthur, reported the "rodent ulcer". In 1900, Edmund Krompecher, identified the histological features as an epithelial carcinoma. The annual incidence of basal cell carcinoma in the United States is approximately 2.8 million which increases with increasing age. Men and white skinned people are affected relatively more, especially in states closer to the equator.There is no well established classification for basal cell carcinoma, however there are few clinical variants which are  nodular, cystic, sclerodermiform, infiltrated, micronodular, superficial, and pigment basal cell carcinoma and fibroepithelioma of Pinkus.Although the exact causes were unknown, the following are some of the factors that have been associated with the development of basal cell carcinoma:  radiation exposure, gene mutations, xeroderma pigmentosa, epidermodysplastic verruciformis, nevoid basal cell carcinoma syndrome, bazex syndrome, rombo syndrome etc. Environmental and genetic risk factors that may predispose to basal cell carcinoma include radiation exposure, physical characteristics, gender, albinism, xeroderma pigmentosum, epidermodysplastic verruciformis, nevoid basal cell carcinoma syndrome, bazex syndrome, rombo syndrome etc. Its morphology is characterized by pearly pink nodules with telangiectasias, rolled borders, and central crusting with or without an ulcerating lesion. The most common cause for the development of the basal cell carcinoma involves radiation exposure and mutations that involve many genes including sonic hedgehog gene, PTCH1 gene, and other gain-of-function mutations which further depend on the subtypes such as nodular, superficial, Infundibulocystic, fibroepithelial, morpheaform, infiltrative, micronodular, and basosquamous basal cell carcinomas. The U.S. Preventive Services Task Force has found no evidence to recommend for or against screening. It is a slow-growing locally invasive lesion with an unlikely risk of metastasis. Most patients are often asymptomatic. The major complication is its recurrence and involvement of surrounding structures. With appropriate treatment, the prognosis is usually excellent. The history and symptoms of basal cell carcinoma include skin growths on sun-exposed skin, mainly in the form of patches that are shiny, pearly bumps, raised edges with central ulceration. They are fragile and may bleed easily. Skin examination usually show papules, plaques, central ulceration with rolled borders, telangiectasias. Skin biopsy is the diagnostic study of choice for basal cell carcinoma. After the suspicious lesion is evaluated, the medical therapy is divided based on low-risk and high-risk basal cell carcinoma patients. Medical therapy consists of topical and systemic therapy. Among topical therapy imiquimod, photodynamic therapy, 5-fluorouracil are included. Systemic therapy consists of sonic hedgehog pathway inhibitors like vismodegib, sonidegib. Types of surgery for basal cell carcinoma involve electrodesiccation and curettage, surgical excision, mohs micrographic surgery, and cryosurgery. The primary prevention of basal cell carcinoma involves avoidance and protection from the sun like using sunscreen lotions, protective clothing, avoid tanning beds etc. A skin biopsy and chemotherapeutic agents such as 5-Fluorouracil or Imiquimod may prevent the further development of basal cell carcinoma.

# Historical Perspective
In 1827, Jacob Arthur, reported the "rodent ulcer". In 1900, Edmund Krompecher, identified the histological features as an epithelial carcinoma.

# Classification
There is no well established classification for basal cell carcinoma, however there are few clinical variants which are  nodular, cystic, sclerodermiform, infiltrated, micronodular, superficial, and pigment basal cell carcinoma and fibroepithelioma of Pinkus.

# Pathophysiology
Basal cell carcinoma is one of the most common skin cancers. It is commonly known as rodent ulcer due to its distinct morphology characterized by pearly pink nodules with telangiectasias, rolled borders, and central crusting with or without an ulcerating lesion. The most common cause for the development of the basal cell carcinoma involves radiation exposure and mutations that involve many genes including sonic hedgehog gene, PTCH1 gene, and other gain-of-function mutations which further depend on the subtypes such as nodular, superficial, Infundibulocystic, fibroepithelial, morpheaform, infiltrative, micronodular, and basosquamous basal cell carcinomas.

# Causes
Although the exact causes were unknown, the following are some of the factors that have been associated with the development of basal cell carcinoma:  radiation exposure, gene mutations, xeroderma pigmentosa, epidermodysplastic verruciformis, nevoid basal cell carcinoma syndrome, bazex syndrome, rombo syndrome etc.

# Differential Diagnosis
There are several differential diagnosis for basal cell carcinoma that may be differentiated clinically or histopathologically including microcystic adnexal carcinoma, trichoepithelioma/trichoblastoma, merkel cell carcinoma, and other squamous cell carcinoma.

# Epidemiology and Demographics
The annual incidence of basal cell carcinoma in the United States is approximately 2.8 million which increases with increasing age. Men and white skinned people are affected relatively more, especially in states closer to the equator.

# Risk Factors
Environmental and genetic risk factors that may predispose to basal cell carcinoma include radiation exposure, physical characteristics, gender, albinism, xeroderma pigmentosum, epidermodysplastic verruciformis, nevoid basal cell carcinoma syndrome, bazex syndrome, rombo syndrome etc.

# Screening
The U.S. Preventive Services Task Force has found no evidence to recommend for or against screening. The American Cancer Society recommends that a health care provider examine the skin every year if the patient is older than 40 years, and every 3 years if the patient is between 20-40 years.

# Natural History, Complications, and Prognosis
It is a slow-growing locally invasive lesion with an unlikely risk of metastasis. Most patients are often asymptomatic. The major complication is its recurrence and involvement of surrounding structures. With appropriate treatment, the prognosis is usually excellent.

# Diagnosis

## Diagnostic Study Of Choice
Skin biopsy is the diagnostic study of choice for basal cell carcinoma.

## Staging
The American Joint Committee on Cancer (AJCC) stages basal cell carcinoma based on the TNM system. T, M, and N are combined into stages, called stage grouping.

## History and Symptoms
The history and symptoms of basal cell carcinoma include skin growths on sun-exposed skin, mainly in the form of patches that are shiny, pearly bumps, raised edges with central ulceration. They are fragile and may bleed easily.

## Physical Examination
Patients with basal cell carcinoma usually have normal general appearance. Skin examination usually show papules, plaques, central ulceration with rolled borders, telangiectasias.

## Laboratory Findings
There are no laboratory tests available to diagnose basal cell carcinoma.

## CT Scan
CT scan is mainly used for the staging of the basal cell carcinoma rather than diagnosing the tumor. CT scan images usually shows hypoattenuating or isoattenuating lesions when compared to adjacent musculature

## MRI
MRI is useful when the tumor has any adjacent bony or perineural invasion. On T1- it appears as an enhancing isointense lesion. On T2- it appears as an hyperintense lesion.

## Other Diagnostic Studies
There are various other techniques for diagnosing basal cell carcinoma, which include Reflectance Confocal Microscopy, Dermatoscopy

# Medical Therapy
After the suspicious lesion is evaluated, the medical therapy is divided based on low-risk and high-risk basal cell carcinoma patients. Medical therapy consists of topical and systemic therapy. Among topical therapy imiquimod, photodynamic therapy, 5-fluorouracil are included. Systemic therapy consists of sonic hedgehog pathway inhibitors like vismodegib, sonidegib.

# Surgery
Types of surgery for basal cell carcinoma involve electrodesiccation and curettage, surgical excision, mohs micrographic surgery, and cryosurgery.

# Primary Prevention
The primary prevention of basal cell carcinoma involves avoidance and protection from the sun like using sunscreen lotions, protective clothing, avoid tanning beds etc

# Secondary Prevention
A skin biopsy and chemotherapeutic agents such as 5-Fluorouracil or Imiquimod may prevent the further development of basal cell carcinoma.