Squamous-cell carcinoma of the lung
| Squamous-cell carcinoma of the lung | |
|---|---|
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| A squamous-cell lung carcinoma developing in the bronchius |
Squamous-cell carcinoma (SCC) of the lung is a histologic type of non-small-cell lung carcinoma (NSCLC). It is the second most prevalent type of lung cancer after lung adenocarcinoma and it originates in the bronchi. Its tumor cells are characterized by a squamous appearance, similar to the one observed in epidermal cells. Squamous-cell carcinoma of the lung is strongly associated with tobacco smoking, more than any other form of NSCLC.[1]
Signs and symptoms
Squamous-cell lung carcinoma share most of the signs and symptoms with other forms of lung cancer. These include worsening cough, including hemoptysis, chest pain, shortness of breath and weight loss. Symptoms may result from local invasion or compression of adjacent thoracic structures such as compression involving the esophagus causing dysphagia, compression involving the laryngeal nerves causing change in voice, or compression involving the superior vena cava causing facial edema. Distant metastases may also cause pain and show symptoms related to other organs.[1]
Causes
Risk factors
Squamous-cell carcinoma of the lung 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.[2] 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.[2]
Mechanism
Pathogenesis
Large scale studies such as The Cancer Genome Atlas (TCGA) have systematically characterized recurrent somatic alterations likely driving lung squamous-cell carcinoma initiation and development.[3][4]
RNA expression profiles
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.[5]
Diagnosis
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.[6]
Classification
The 2015 WHO classification of lung tumors[7] divided squamous cell lung carcinomas into 3 categories: keratinizing, non-keratinizing and basaloid. Keratinizing SCC harbor features of keratinization; non-keratinizing SCC lack such features but show other squamous markers, such as p40 and p63; finally, basaloid SCC is a rare subset of poorly differentiated squamous cell lung carcinoma. Previous variants such as papillary, small-cell and clear-cell SCC were discarded from the current classification as these subtypes are very uncommon. There is no clear evidence of prognostic significance to the subtyping of lung squamous cell carcinoma.[7]
Treatment
Epidemiology
References
- ^ a b "Non-Small Cell Lung Cancer Treatment". National Cancer Institute. 1980-01-01. Retrieved 2019-02-28.
- ^ a b Kenfield, S. A.; Wei, E. K.; Stampfer, M. J.; Rosner, B. A.; Colditz, G. A. (2008). "Comparison of aspects of smoking among the four histological types of lung cancer". Tobacco Control. 17 (3): 198–204. doi:10.1136/tc.2007.022582. PMC 3044470. PMID 18390646.
- ^ The Cancer Genome Atlas Research Network (September 2012). "Comprehensive genomic characterization of squamous cell lung cancers". Nature. 489 (7417): 519–525. doi:10.1038/nature11404. ISSN 1476-4687.
- ^ Meyerson, Matthew; Govindan, Ramaswamy; Schreiber, Robert; Artyomov, Maxim N.; Mills, Gordon B.; Yena, Peggy; Sherman, Mark; Shelton, Troy; Shelton, Candace (June 2016). "Distinct patterns of somatic genome alterations in lung adenocarcinomas and squamous cell carcinomas". Nature Genetics. 48 (6): 607–616. doi:10.1038/ng.3564. ISSN 1546-1718.
- ^ Wilkerson, MD; Yin, X; Hoadley, KA; Liu, Y; Hayward, MC; Cabanski, CR; Muldrew, K; Miller, CR; Randell, SH; Socinski, M. A.; Parsons, A. M.; Funkhouser, W. K.; Lee, C. B.; Roberts, P. J.; Thorne, L.; Bernard, P. S.; Perou, C. M.; Hayes, D. N. (2010). "Lung squamous cell carcinoma mRNA expression subtypes are reproducible, clinically important, and correspond to normal cell types". Clinical Cancer Research. 16 (19): 4864–75. doi:10.1158/1078-0432.CCR-10-0199. PMC 2953768. PMID 20643781.
- ^ Entire section, if not else specified, is taken from Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson (2007). "Ch. 13, box on morphology of squamous cell carcinoma". Robbins Basic Pathology (8th ed.). Philadelphia: Saunders. ISBN 978-1-4160-2973-1.
- ^ a b Travis, William D.; Brambilla, Elisabeth; Nicholson, Andrew G.; Yatabe, Yasushi; Austin, John H. M.; Beasley, Mary Beth; Chirieac, Lucian R.; Dacic, Sanja; Duhig, Edwina (September 2015). "The 2015 World Health Organization Classification of Lung Tumors: Impact of Genetic, Clinical and Radiologic Advances Since the 2004 Classification". Journal of Thoracic Oncology: Official Publication of the International Association for the Study of Lung Cancer. 10 (9): 1243–1260. doi:10.1097/JTO.0000000000000630. ISSN 1556-1380. PMID 26291008.