Adenocarcinoma of the lung overview

# Overview
Adenocarcinoma of the lung is a common histological form of lung cancer. Adenocarcinoma of the lung may be classified according to WHO into 8 subtypes: Lepidic, acinar, papillary, micropapillary, solid, colloid, fetal, enteric adenocarcinoma. Adenocarcinoma of the lung may be classified according to IASLC/ATS/ERS into 3 main types: adenocarcinoma in situ, minimally invasive adenocarcinoma, invasive adenocarcinoma. On gross pathology, peripheral multifocal lesions is the characteristic finding of adenocarcinoma of the lung. On microscopic histopathological analysis, nuclear atypia, eccentrically placed nuclei, abundant cytoplasm, and conspicuous nucleoli are characteristic findings of adenocarcinoma of the lung. Genes involved in the pathogenesis of adenocarcinoma of the lung include EGFR, HER2, KRAS, ALK, and BRAF. Common risk factors in the development of adenocarcinoma of the lung include smoking, family history of lung cancer, high levels of air pollution, radiation therapy to the chest, radon gas, asbestos, occupational exposure to chemical carcinogens, and previous lung disease. The incidence of adenocarcinoma of the lung is approximately 22.1 per 100,000 individuals worldwide. Adenocarcinoma of the lung affects men and women equally. Patients of all age groups may develop adenocarcinoma of the lung. Common symptoms of adenocarcinoma of the lung include dyspnea, hemoptysis, chronic coughing, chest pain, cachexia, dysphonia, and paraneoplastic syndromes. Adenocarcinoma of the lung may be classified into several subtypes based on TNM and UICC staging system. The predominant therapy for adenocarcinoma of the lung is surgical resection. Adjunctive chemotherapy, radiation therapy, and target therapy may be required. Common complications of adenocarcinoma of the lung include breathing difficulties, pneumonia, pleural effusion, metastasis, and Horner's syndrome. The prognosis of adenocarcinoma of the lung varies with the staging of tumor; Stage IA have the most favorable prognosis. The presence of metastasis is associated with a particularly poor prognosis.

# Classification
Adenocarcinoma of the lung may be classified according to WHO into 5 subtypes: mixed, acinar, papillary, bronchioloalveolar carcinoma, and solid adenocarcinoma. Adenocarcinoma of the lung may be classified according to IASLC/ATS/ERS into 6 subtypes: pre-invasive lesions, atypical adenomatous hyperplasia, adenocarcinoma in situ, minimally invasive adenocarcinoma, invasive adenocarcinoma, and variants of invasive adenocarcinoma. Adenocarcinoma of the lung may be classified into several subtypes based on TNM and UICC staging system.

# Pathophysiology
On gross pathology, peripheral multifocal lesions is the characteristic finding of adenocarcinoma of the lung. On microscopic histopathological analysis, nuclear atypia, eccentrically placed nuclei, abundant cytoplasm, and conspicuous nucleoli are characteristic findings of adenocarcinoma of the lung. Genes involved in the pathogenesis of adenocarcinoma of the lung include EGFR, HER2, KRAS, ALK, and BRAF.

# Cause
Adenocarcinoma of the lung may caused by genetic mutations, including EGFR (7p11), KRAS (12p12), BRAF (7q34), and PIK3CA (3q26).

# Differential Diagnosis
Adenocarcinoma of the lung must be differentiated from atypical adenomatous hyperplasia of the lung, adenocarcinoma in situ, squamous cell carcinoma of the lung, small cell carcinoma of the lung, malignant mesothelioma, and metastatic adenocarcinoma.

# Epidemiology and Demographics
The incidence of adenocarcinoma of the lung is approximately 22.1 per 100,000 individuals worldwide. Adenocarcinoma of the lung affects men and women equally. Patients of all age groups may develop adenocarcinoma of the lung.

# Risk Factors
Common risk factors in the development of adenocarcinoma of the lung include smoking, family history of lung cancer, high levels of air pollution, radiation therapy to the chest, radon gas, asbestos, occupational exposure to chemical carcinogens, and previous lung disease.

# Screening
According to the clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF), screening for lung cancer by low-dose computed tomography (LDCT) is recommended every year among smokers and former smokers who are between 55 to 80 years old and who have smoked 30 pack-years or more and either continue to smoke or have quit within the past 15 years (grade B recommendation).  According to the clinical practice guideline issued by the American College of Chest Physicians (CHEST) in 2013, screening for lung cancer by low-dose CT (LDCT) is recommended every year among smokers and former smokers who are age 55 to 74 and who have smoked for 30 pack-years or more and either continue to smoke or have quit within the past 15 years.

# Natural history, Complications, and Prognosis
Common complications of adenocarcinoma of the lung include breathing difficulties, pneumonia, pleural effusion, metastasis, and Horner's syndrome. The prognosis of adenocarcinoma of the lung varies with the staging of tumor; Stage IA have the most favorable prognosis. The presence of metastasis is associated with a particularly poor prognosis.

# Diagnosis

## Diagnostic Study of Choice
Biopsy is helpful in the diagnosis of adenocarcinoma of the lung.

## History and Symptoms
Common symptoms of adenocarcinoma of the lung include dyspnea, hemoptysis, chronic coughing, chest pain, cachexia, dysphonia, and paraneoplastic syndromes.

## Physical Examination
Common physical examination findings of adenocarcinoma of the lung include tachypnea, decreased breath sounds, and lethargy.

## Laboratory Findings

## Electrocardiogram

## X Ray
Chest x-ray may be helpful in the diagnosis of adenocarcinoma of the lung. Findings on x-ray suggestive of adenocarcinoma of the lung include mass, widening of the mediastinum, atelectasis, consolidation, and pleural effusion.

## Echocardiography and Ultrasound
Ultrasound may be helpful in the diagnosis of pleural effusion among patients with adenocarcinoma of the lung.

## CT
Chest CT scan may be helpful in the diagnosis of adenocarcinoma of the lung. Finding on CT scan suggestive of adenocarcinoma of the lung is a lung nodule with a rounded or irregular region of increased attenuation.

## MRI
There are no MRI findings associated with adenocarcinoma of the lung.

## Other Imaging Findings
Other diagnostic studies for adenocarcinoma of the lung include bone scintigraphy, PET scan, and pulmonary ventilation/perfusion scan.

## Other Diagnostic Studies
Other diagnostic studies for adenocarcinoma of the lung include molecular testing and endoscopy.

# Treatment

## Medical Therapy
The predominant therapy for adenocarcinoma of the lung is surgical resection. Adjunctive chemotherapy, radiation therapy, and target tharapy may be required.

## Interventions

## Surgery
Surgery is the mainstay of treatment for adenocarcinoma of the lung.

## Primary Prevention
Effective measures for the primary prevention of adenocarcinoma of the lung include smoking cessation, eliminating secondhand smoke, reducing or eliminating exposure to radon, and reducing or eliminating occupational exposure to lung carcinogens.

## Secondary Prevention