Signs and symptoms which may suggest lung cancer include:

- Respiratory symptoms: coughing, coughing up blood, wheezing, or shortness of breath

- Systemic symptoms: weight loss, weakness, fever, or clubbing of the fingernails

- Symptoms due to the cancer mass pressing on adjacent structures: chest pain, bone pain, superior vena cava obstruction, or difficulty swallowing

If the cancer grows in the airways, it may obstruct airflow, causing breathing difficulties. The obstruction can lead to accumulation of secretions behind the blockage, and predispose to pneumonia.

Depending on the type of tumor, paraneoplastic phenomena—symptoms not due to the local presence of cancer—may initially attract attention to the disease. In lung cancer, these phenomena may include hypercalcemia, syndrome of inappropriate antidiuretic hormone (SIADH, abnormally concentrated urine and diluted blood), ectopic ACTH production, or Lambert–Eaton myasthenic syndrome (muscle weakness due to autoantibodies). Tumors in the top of the lung, known as Pancoast tumors, may invade the local part of the sympathetic nervous system, leading to Horner's syndrome (dropping of the eyelid and a small pupil on that side), as well as damage to the brachial plexus.

Many of the symptoms of lung cancer (poor appetite, weight loss, fever, fatigue) are not specific. In many people, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. Symptoms that suggest the presence of metastatic disease include weight loss, bone pain and neurological symptoms (headaches, fainting, convulsions, or limb weakness). Common sites of spread include the brain, bone, adrenal glands, opposite lung, liver, pericardium, and kidneys. About 10% of people with lung cancer do not have symptoms at diagnosis; these cancers are incidentally found on routine chest radiography.

Lung cancer, also known as lung carcinoma, is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. This growth can spread beyond the lung by the process of metastasis into nearby tissue or other parts of the body. Most cancers that start in the lung, known as primary lung cancers, are carcinomas. The two main types are small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC). The most common symptoms are coughing (including coughing up blood), weight loss, shortness of breath, and chest pains.

The vast majority (85%) of cases of lung cancer are due to long-term tobacco smoking. About 10–15% of cases occur in people who have never smoked. These cases are often caused by a combination of genetic factors and exposure to radon gas, asbestos, second-hand smoke, or other forms of air pollution. Lung cancer may be seen on chest radiographs and computed tomography (CT) scans. The diagnosis is confirmed by biopsy which is usually performed by bronchoscopy or CT-guidance.

Avoidance of risk factors, including smoking and air pollution, is the primary method of prevention. Treatment and long-term outcomes depend on the type of cancer, the stage (degree of spread), and the person's overall health. Most cases are not curable. Common treatments include surgery, chemotherapy, and radiotherapy. NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiotherapy.

Worldwide in 2012, lung cancer occurred in 1.8 million people and resulted in 1.6 million deaths. This makes it the most common cause of cancer-related death in men and second most common in women after breast cancer. The most common age at diagnosis is 70 years. Overall, 17.4% of people in the United States diagnosed with lung cancer survive five years after the diagnosis, while outcomes on average are worse in the developing world.

Nearly 40% of lung cancers in the US are adenocarcinoma, which usually originates in peripheral lung tissue. Most cases of adenocarcinoma are associated with smoking; however, among people who have smoked fewer than 100 cigarettes in their lifetimes ("never-smokers"), adenocarcinoma is the most common form of lung cancer. Its incidence has been increasing in many developed Western nations in the past few decades, where it has become the most common major type of lung cancer in smokers (replacing squamous cell lung carcinoma) and in lifelong nonsmokers. According to the Nurses' Health Study, the risk of adenocarcinoma of the lung increases substantially after a long duration of previous tobacco smoking, with a previous smoking duration of 30 to 40 years giving a relative risk of approximately 2.4 compared to never-smokers, and a duration of more than 40 years giving a relative risk of approximately 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, adenocarcinomas grow more slowly and form smaller masses than the other subtypes. However, they tend to form metastases widely at an early stage. Adenocarcinoma is a non-small cell lung carcinoma, and as such, it is not as responsive to radiation therapy as is small cell lung carcinoma, but is rather treated surgically, for example by pneumonectomy or lobectomy.

Patients typically present with a non-productive cough and weight loss.

It most often arises centrally in larger bronchi, and while it often metastasizes to locoregional lymph nodes (particularly the hilar nodes) early in its course, it generally disseminates outside the thorax somewhat later than other major types of lung cancer. Large tumors may undergo central necrosis, resulting in cavitation. A squamous-cell carcinoma is often preceded for years by squamous-cell metaplasia or dysplasia in the respiratory epithelium of the bronchi, which later transforms to carcinoma in situ.

In carcinoma in situ, atypical cells may be identified by cytologic smear test of sputum, bronchoalveolar lavage or samples from endobronchial brushings. However, squamous-cell carcinoma in situ is asymptomatic and undetectable on X-ray radiographs.

Eventually, it becomes symptomatic, usually when the tumor mass begins to obstruct the lumen of a major bronchus, often producing distal atelectasis and infection. Simultaneously, the lesion invades into the surrounding pulmonary substance. On histopathology, these tumors range from well differentiated, showing keratin pearls and cell junctions, to anaplastic, with only minimal residual squamous-cell features.

Non-small-cell lung carcinoma (NSCLC) is any type of epithelial lung cancer other than small cell lung carcinoma (SCLC). NSCLC accounts for about 85% of all lung cancers. As a class, NSCLCs are relatively insensitive to chemotherapy, compared to small cell carcinoma. When possible, they are primarily treated by surgical resection with curative intent, although chemotherapy is increasingly being used both pre-operatively (neoadjuvant chemotherapy) and post-operatively (adjuvant chemotherapy).

Small-cell carcinoma of the lung usually presents in the central airways and infiltrates the submucosa leading to narrowing of bronchial airways. Common symptoms include cough, dyspnea, weight loss, and debility. Over 70% of patients with small-cell carcinoma present with metastatic disease; common sites include liver, adrenals, bone, and brain.

Due to its high grade neuroendocrine nature, small-cell carcinomas can produce ectopic hormones, including adrenocorticotropic hormone (ACTH) and anti-diuretic hormone (ADH). Ectopic production of large amounts of ADH leads to syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH).

Lambert-Eaton myasthenic syndrome (LEMS) is a well-known paraneoplastic condition linked to small-cell carcinoma.

Squamous-cell carcinoma (SCC) of the lung is a type of non-small-cell lung carcinoma and is more common in men than in women. It is closely correlated with a history of tobacco smoking, more so than most other types of lung cancer. According to the Nurses' Health Study, the relative risk of SCC is approximately 5.5, both among those with a previous duration of smoking of 1 to 20 years, and those with 20 to 30 years, compared to never-smokers. The relative risk increases to approximately 16 with a previous smoking duration of 30 to 40 years, and approximately 22 with more than 40 years.

Many of the symptoms of NSCLC can be signs of other diseases, but having chronic or overlapping symptoms may be a signal of the presence of the disease. Some symptoms are indicators of less advanced cases while some may signal that the cancer has spread. Some of the symptoms of less advanced cancer include chronic cough, coughing up blood, chest pain, hoarseness, shortness of breath, wheezing, chest pain, weight loss, and loss of appetite. A few more symptoms associated with the early progression of the disease are feeling weak, being very tired, having trouble swallowing, swelling in the face or neck, and continuous or recurring infections like bronchitis or pneumonia. Signs of more advanced cases include bone pain, nervous system changes (headache, weakness, dizziness, balance problems, seizures), jaundice, lumps near the surface of the body, numbness of extremities due to Pancoast Syndrome, and nausea, vomiting and constipation brought on by hypercalcemia. Some more of the symptoms that indicate further progression of the cancer include shortness of breath, superior vena cava syndrome, trouble swallowing, large amounts of mucus, weakness, fatigue, and hoarseness.

Adenocarcinomas are highly heterogeneous tumors. Several major histological subtypes are currently recognized by the WHO and IASLC/ATS/ERS

- Non-invasive or minimally invasive adenocarcinoma

- Adenocarcinoma in situ of the lung (Bronchioalveolar carcinoma)

- Minimally invasive adenocarcinoma of the lung

- Invasive adenocarcinoma

- Acinar predominant adenocarcinoma

- Papillary predominant adenocarcinoma

- Micropapillary predominant adenocarcinoma

- Solid predominant adenocarcinoma

- Invasive mucinous adenocarcinoma

In as many as 80% of tumors that are extensively sampled, components of more than one of these subtypes will be recognized. In such cases, resected tumors should be classified by comprehensive histological subtyping. Using increments of 5% to describe the amount of each subtype present, the predominant subtype is used to classify the whole tumor. The predominant subtype is prognostic for survival after complete resection.

Signet ring and clear cell adenocarcinoma are no longer histological subtypes, but rather cytological features that can occur in tumour cells of multiple histological subtypes, most often solid adenocarcinoma.

Some variants are not clearly recognized by the WHO and IASLC/ATS/ERS classification:

- Enteric adenocarcinoma of the lung

- Cribriform adenocarcinoma of the lung

Small-cell carcinoma (also known as "small-cell lung cancer", or "oat-cell carcinoma") is a type of highly malignant cancer that most commonly arises within the lung, although it can occasionally arise in other body sites, such as the cervix, prostate, and gastrointestinal tract. Compared to non-small cell carcinoma, small cell carcinoma has a shorter doubling time, higher growth fraction, and earlier development of metastases.

Lung cancers have been historically classified using two major paradigms. Histological classification systems group lung cancers according to the appearance of the cells and surrounding tissues when they are viewed under a microscope. Clinical classification systems divide lung cancers into groups based on medical criteria, particularly their response to different treatment regimens.

Before the mid-1900s, lung cancer was considered to be a single disease entity, with all forms treated similarly. In the 1960s, small cell lung carcinoma (SCLC) was recognized as a unique form of lung cancer, based both on its appearance (histology) and its clinical properties, including much greater susceptibility to chemotherapy and radiation, more rapid growth rate, and its propensity to metastasize widely early on in its course. Since then, most oncologists have based patient treatment decisions on a dichotomous division of lung cancers into SCLC and non-small cell lung carcinomas (NSCLC), with the former being treated primarily with chemoradiation, and the latter with surgery.

An explosion of new knowledge, accumulated mainly over the last 20 years, has proved that lung cancers should be considered an extremely heterogeneous family of neoplasms with widely varying genetic, biological, and clinical characteristics, particularly their responsiveness to the large number of newer treatment protocols. Well over 50 different histological variants are now recognized under the 2004 revision of the World Health Organization ("WHO-2004") typing system, currently the most widely used lung cancer classification scheme. Recent studies have shown beyond doubt that the old clinical classification paradigm of "SCLC vs. NSCLC" is now obsolete, and that correct "subclassification" of lung cancer cases is necessary to assure that lung cancer patients receive optimum management.

Approximately 98% of lung cancers are carcinoma, which are tumors composed of cells with epithelial characteristics. LCLC's are one of 8 major groups of lung carcinomas recognized in WHO-2004:

- Squamous cell carcinoma

- Small cell carcinoma

- Adenocarcinoma

- Large cell carcinoma

- Adenosquamous carcinoma

- Sarcomatoid carcinoma

- Carcinoid tumor

- Salivary gland-like carcinoma

In WHO-2004, BACs are one of four specific histologic subtypes of lung adenocarcinoma, along with acinar adenocarcinoma, papillary adenocarcinoma, and solid adenocarcinoma with mucin production. However, approximately 80% of adenocarcinomas are found to contain two (or more) of these four subtypes. Multiphasic tumors such as these are classified into a fifth "subtype", termed adenocarcinoma with mixed subtypes.

There are other classification systems that have been proposed for lung cancers, including BACs and other forms of adenocarcinoma. The Noguchi classification system for small adenocarcinomas has received considerable attention, particularly in Japan, but has not been nearly as widely applied and recognized as the WHO system.

Like other forms of lung carcinoma, BAC possesses unique clinical and pathological features, prognosis, and responses to different treatments.

In situ pulmonary adenocarcinoma (AIS), previously called "Bronchioloalveolar carcinoma" (BAC), is a term describing certain variants of lung cancer arising in the distal bronchioles or alveoli that initially exhibit a specific non-invasive growth pattern. BAC is a type of non-small-cell lung cancer (NSCLC). AIS is defined as a small (≤3 cm) solitary tumour with pure alveolar epithelial appearance (lepidic growth), lacking any invasion of the interstitium. If completely resected, the prognosis of surgically treated AIS is 100%.

Lung carcinoids typically present with a cough or hemoptysis. Findings may closely mimic malignant tumours of the lung, i.e. lung cancer.

Typical pulmonary carcinoid tumour is a subtype of pulmonary carcinoid tumour. It is an uncommon low-grade malignant lung mass that is most often in the central airways of the lung.

It is also known as typical lung carcinoid tumour, lung carcinoid, and typical lung carcinoid.

Adenosquamous lung carcinoma (AdSqLC) is a biphasic malignant tumor arising from lung tissue that is composed of at least 10% by volume each of squamous cell carcinoma (SqCC) and adenocarcinoma (AdC) cells.

FA can produce repeated hemoptysis, possibly related to cavitation of the tumor.

Other presenting symptoms described have included: flu-like syndrome with cough and fever,

Pulmonary neuroendocrine tumors are neuroendocrine tumors localized to the lung: bronchus or pulmonary parenchyma.

Pulmonary neuroendocrine tumors include a spectrum of tumors from the low-grade typical pulmonary carcinoid tumor and intermediate-grade atypical pulmonary carcinoid tumor to the high-grade pulmonary large cell neuroendocrine carcinoma (LCNEC) and pulmonary small cell carcinoma (SCLC), with significant clinical, epidemiologic and genetic differences.

LCC is, in effect, a "diagnosis of exclusion", in that the tumor cells lack light microscopic characteristics that would classify the neoplasm as a small-cell carcinoma, squamous-cell carcinoma, adenocarcinoma, or other more specific histologic type of lung cancer.

LCC is differentiated from small-cell lung carcinoma (SCLC) primarily by the larger size of the anaplastic cells, a higher cytoplasmic-to-nuclear size ratio, and a lack of "salt-and-pepper" chromatin.

Synonyms for FA include well differentiated fetal adenocarcinoma, high-grade fetal adenocarcinoma, pulmonary adenocarcinoma

of fetal type, and pulmonary endodermal tumour resembling fetal lung.

Clinical factors predicting the diagnosis of malignant pleural effusions are symptoms lasting more than 1 month and the absence of fever.

Lung cancer is an extremely heterogeneous family of malignant neoplasms, with well over 50 different histological variants recognized under the 4th revision of the World Health Organization (WHO) typing system ("WHO-2004"), currently the most widely used lung cancer classification scheme. Because these variants have differing genetic, biological, and clinical properties, including response to treatment, correct classification of lung cancer cases are necessary to assure that lung cancer patients receive optimum management.

The WHO-2004 scheme groups lung carcinomas into 8 major types:

- Squamous cell carcinoma

- Small cell carcinoma

- Adenocarcinoma

- Large cell carcinoma

- Adenosquamous carcinoma

- Sarcomatoid carcinoma

- Carcinoid tumor

- Salivary gland-like carcinoma

EMECL is considered a subtype of salivary gland-like carcinoma, tumors so named because their histological appearance and characteristics closely resemble malignant neoplasms arising in the major and minor salivary glands.

"Lung tumors" are neoplastic tumors of the lung These include:

Primary tumors of the lung/pulmonary system:

- Bronchial leiomyoma, a rare, benign tumor

- Lung cancer, the term commonly used to refer to "carcinoma of the lung"

- Pulmonary carcinoid tumor

- Pleuropulmonary blastoma

- Neuroendocrine tumors of the lung

- Lymphomas of the lung.

- Sarcomas of the lung.

- Some rare vascular tumors of the lung

Non-lung tumors which may grow into the lungs:

- Mediastinal tumors

- Pleural tumors

Metastasis or secondary tumors/neoplasms with other origin:

- Metastasis to the lung

A pattern of multiple small nodular metastases has been described as miliary carcinosis which has a radiographic appearance similar to miliary tuberculosis.