| Non-small-cell lung carcinoma | |
|---|---|
| Classification and external resources | |
Micrograph of a squamous carcinoma, a type of non-small-cell lung carcinoma. FNA specimen. Pap stain. |
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| MedlinePlus | 007194 |
| eMedicine | med/1333 |
| MeSH | D002289 |
Non-small-cell lung carcinoma (NSCLC) is any type of epithelial lung cancer other than small cell lung carcinoma (SCLC). 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).
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The most common types of NSCLC are squamous cell carcinoma, large cell carcinoma, and adenocarcinoma, but there are several other types that occur less frequently, and all types can occur in unusual histologic variants and as mixed cell-type combinations.[2]
Sometimes the phrase "non-small-cell lung cancer" ("not otherwise specified", or NOS) is used generically, usually when a more specific diagnosis cannot be made. This is most often the case when a pathologist examines a small amount of malignant cells or tissue in a cytology or biopsy specimen.[2]
Lung cancer in never-smokers is almost universally NSCLC, with a sizeable majority being adenocarcinoma.[3]
On relatively rare occasions, malignant lung tumors are found to contain components of both SCLC and NSCLC. In these cases, the tumors should be classified as combined small cell lung carcinoma (c-SCLC),[4] and are (usually) treated like "pure" SCLC.[5]
Squamous cell carcinoma (SCC) of the lung 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.[6] 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.[6]
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.[7]
Currently, four variants (papillary, small cell, clear cell, and basaloid) of squamous cell carcinoma of the lung are recognized. Of these variants, there is some evidence that the basaloid[8] and poorly differentiated small-cell variants [4] may have worse prognoses than "conventional" squamous cell carcinomas. The papillary variant occurs more frequently as a primarily superficial, endobronchial lesion, with a modestly better prognosis[4][9] Very little data is currently available on the clear cell variant of squamous cell carcinoma, and no consensus has been reached on the prognostic implications of clear cell changes in lung cancer[10][11]
Recently, four mRNA expression subtypes (primitive, basal, secretory, and classical) were identified and validated within squamous cell carcinoma. The primitive subtype correlates with worse patient survival. These subtypes, defined by intrinsic expression differences, provide a possible foundation for improved patient prognosis and research into individualized therapies.[12]
Large cell lung carcinoma (LCLC) is a heterogeneous group of undifferentiated malignant neoplasms originating from transformed epithelial cells in the lung. LCLC's have typically comprised between around 10% of all NSCLC in the past, although newer diagnostic techniques seem to be reducing the incidence of diagnosis of "classic" LCLC in favor of more poorly differentiated squamous cell carcinomas and adenocarcinomas.[13] LCLC 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. LCLC 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.
Adenocarcinoma of the lung is currently the most common type of lung cancer in "never smokers" (lifelong non-smokers).[14] Adenocarcinomas account for approximately 40% of lung cancers. Historically, adenocarcinoma was more often seen peripherally in the lungs than small cell lung cancer and squamous cell lung cancer, both of which tended to be more often centrally located.[15][16] Interestingly, however, recent studies suggest that the "ratio of centrally-to-peripherally occurring" lesions may be converging toward unity for both adenocarcinoma and squamous cell carcinoma.
The American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC) recommend TNM staging, using a uniform scheme for non-small cell lung carcinoma, small-cell lung carcinoma and broncho-pulmonary carcinoid tumors.[17] AJCC has provided an accessible poster version of these copyrighted TNM descriptors to which readers are directed.[17] Extensive presentation of prognostic data for both 6th and 7th edition individual TNM descriptors and overall groups is available.[18]
More than one kind of treatment is often used, depending on the stage of the cancer, the individual's overall health, age, response to chemotherapy, and other factors such as the likely side effects of the treatment.
NSCLCs are usually not very sensitive to chemotherapy[19] and/or radiation, so surgery is the treatment of choice if diagnosed at an early stage, often with adjuvant (ancillary) chemotherapy involving cisplatin. Other treatment choices are chemotherapy, radiation therapy (radiotherapy), and targeted therapy.
New methods of giving radiation treatment allow doctors to be more accurate in treating lung cancers. This means less radiation affects nearby healthy tissues. New methods include Gamma knife, Cyberknife and stereotactic radiosurgery (SRS).
Other treatments are radiofrequency ablation[20] and chemoembolization.[21]
A wide variety of chemotherapies are used in advanced (metastatic) NSCLC.[22] Some patients with particular mutations in the EGFR gene respond to EGFR tyrosine kinase inhibitors such as gefitinib.[23]
There are many phase III clinical trials of new therapies for advanced NSCLC,[24] including intedanib (BIBF 1120).
About 7% of NSCLC have EML4-ALK translocations; these may benefit from ALK inhibitors which are in clinical trials.[25] Crizotinib gained FDA approval in Aug 2011.
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