Adenocarcinoma of the lung

Adenocarcinoma of the lung is the most common type of lung cancer, and like other forms of lung cancer, it is characterized by distinct cellular and molecular features. It is classified as one of several non-small cell lung cancers (NSCLC), to distinguish it from small cell lung cancer which has a different behavior and prognosis. Lung adenocarcinoma is further classified into several subtypes and variants. The signs and symptoms of this specific type of lung cancer are similar to other forms of lung cancer, and patients most commonly complain of persistent cough and shortness of breath. Adenocarcinoma is more common in patients with a history of cigarette smoking, and is the most common form of lung cancer in younger women and Asian populations. The pathophysiology of adenocarcinoma is complicated, but generally follows a histologic progression from cells found in healthy lungs to distinctly dysmorphic, or irregular, cells. There are several distinct molecular and genetic pathways that contribute to this progression. Like many lung cancers, adenocarcinoma of the lung is often advanced by the time of diagnosis. Once a lesion or tumor is identified with various imaging modalities, such as computed tomography (CT) or X-ray, a biopsy is required to confirm the diagnosis. Treatment of this lung cancer is based upon the specific subtype and the extent of spread from the primary tumor. Surgical resection, chemotherapy, radiotherapy, targeted therapy and immunotherapy are used in attempt to eradicate the cancerous cells based upon these factors. Adenocarcinoma of the lung is the most common type of lung cancer, and like other forms of lung cancer, it is characterized by distinct cellular and molecular features. It is classified as one of several non-small cell lung cancers (NSCLC), to distinguish it from small cell lung cancer which has a different behavior and prognosis. Lung adenocarcinoma is further classified into several subtypes and variants. The signs and symptoms of this specific type of lung cancer are similar to other forms of lung cancer, and patients most commonly complain of persistent cough and shortness of breath. Adenocarcinoma is more common in patients with a history of cigarette smoking, and is the most common form of lung cancer in younger women and Asian populations. The pathophysiology of adenocarcinoma is complicated, but generally follows a histologic progression from cells found in healthy lungs to distinctly dysmorphic, or irregular, cells. There are several distinct molecular and genetic pathways that contribute to this progression. Like many lung cancers, adenocarcinoma of the lung is often advanced by the time of diagnosis. Once a lesion or tumor is identified with various imaging modalities, such as computed tomography (CT) or X-ray, a biopsy is required to confirm the diagnosis. Treatment of this lung cancer is based upon the specific subtype and the extent of spread from the primary tumor. Surgical resection, chemotherapy, radiotherapy, targeted therapy and immunotherapy are used in attempt to eradicate the cancerous cells based upon these factors. The majority of patients who are diagnosed with lung cancer usually present with locally advanced or metastatic disease. Only about one third of patients have stage I disease when diagnosed. The symptoms that the patient exhibits usually reflect the extent of the cancer's spread. Lung cancers that are discovered early may cause symptoms localized to the respiratory system. However, lung cancer that is advanced will cause patients to experience additional signs and symptoms secondary to the cancer spreading to other organ systems. In order of highest frequency, the most common signs of lung cancer include: Clinicians should have a high level of suspicion for lung cancer, especially in patients with a smoking history. Patients with recurring or unresolving lung infections (e.g. bronchitis and pneumonia) that are unresponsive to antibiotics should also be further evaluated for lung cancer. In nonsmokers, women and East Asians are more likely to present with symptoms of an underlying lung cancer at younger ages.Importantly, many of these signs are commonly due to other causes which are not cancer. A detailed medical history should be obtained from each patient to determine the relevance of further diagnostic workup and management. Adenocarcinoma, like other forms of lung cancer, is usually advanced or metastatic at time of diagnosis. Patients may complain of signs or symptoms outside of the respiratory tract that represent a hematologic or metabolic complication of the malignancy without, however, resulting necessarily from obstruction or metastasis. These go under the name of paraneoplastic syndromes, which often indicate advanced disease and worse prognosis. The most common paraneoplastic syndromes associated with adenocarcinoma of the lung are described below: According to the Nurses' Health Study, the risk of pulmonary adenocarcinoma increases substantially after a long duration of tobacco smoking: smokers with a previous smoking duration of 30–40 years are more than twice as likely to develop lung adenocarcinoma compared to never-smokers (relative risk of approximately 2.4); a duration of more than 40 years increases relative risk to 5. This cancer usually is seen peripherally in the lungs, as opposed to small cell lung cancer and squamous cell lung cancer, which both tend to be more centrally located, although it may also occur as central lesions. For unknown reasons, it often arises in relation to peripheral lung scars. The current theory is that the scar probably occurred secondary to the tumor, rather than causing the tumor. The adenocarcinoma has an increased incidence in smokers, and is the most common type of lung cancer seen in non-smokers and women. The peripheral location of adenocarcinoma in the lungs may be due to the use of filters in cigarettes which prevent the larger particles from entering the lung. Deeper inhalation of cigarette smoke results in peripheral lesions that are often the case in adenocarcinomas of the lung. Generally, adenocarcinoma grows more slowly and forms smaller masses than the other subtypes. However, it tends to metastasize at an early stage. Large scale studies such as The Cancer Genome Atlas (TCGA) have systematically characterized recurrent somatic alterations likely driving lung adenocarcinoma initiation and development. Since smoking is a strong mutagenic factor, lung adenocarcinoma is one of the tumor types with the highest number of mutations. Common somatic mutations in lung adenocarcinoma affect many oncogenes and tumor suppressor genes, including TP53 (mutated in 46% of cases), EGFR (27%), KRAS (32%), KEAP1, STK11 and NF1. EGFR and KRAS mutations tend to appear in a mutually exclusive fashion. KRAS mutations are associated with smoking habits, whereas EGFR mutations occur more frequently in females, people of Asian ethnicity and never-smokers. Copy number amplifications in oncogenes such as TERT, MDM2, EGFR, MET, and MYC have been reported, as well as deletions of tumor suppressor genes such as CDKN2A.