Adenocarcinoma of the lung

From Wikipedia, the free encyclopedia - View original article

 
Jump to: navigation, search

Adenocarcinoma of the lung is a common histological form of lung cancer that contains certain distinct malignant tissue architectural, cytological, or molecular features, including gland and/or duct formation and/or production of significant amounts of mucus.[1]

Classification[edit]

Pie chart showing incidence of adenocarcinoma of the lung (shown in yellow) as compared to other lung cancer types, with fractions of non-smokers versus smokers shown for each type.[2]

Lung cancer is an extremely heterogeneous family of malignant neoplasms,[3] with over 50 different histological variants recognized in the 4th revision of the World Health Organization (WHO) typing system, currently the most widely used lung cancer classification scheme.[1] 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.[4][5] While a small percentage of lung cancers are mainly sarcoma or tumors of hematopoietic or germ cell origin,[6] approximately 98% of lung cancers are carcinoma, which are tumors composed of cells with epithelial characteristics.[6] Adenocarcinomas (AdC's) are one of 8 major groups of lung carcinomas recognized in WHO-2004:[1]

Epidemiology[edit]

Adenocarcinoma is the most common type of lung cancer in lifelong non-smokers.[7] 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.[1] 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.[8]

Adenocarcinomas account for approximately 40% of lung cancers.[6]

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,[9][6] although it may also occur as central lesions.[9] 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.[9] The adenocarcinoma has an increased incidence in smokers, and is the most common type of lung cancer seen in non-smokers and women.[9] The peripheral location of adenocarcinoma in the lungs is due to the use of filters in cigarettes which prevent the larger particles from entering the lung.[clarification needed][10][11] 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.[9] However, they tend to form metastases widely at an early stage.[9] 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.[9]

Histopathology[edit]

Adenocarcinomas are highly heterogeneous tumors, and several major histological subtypes are currently recognized:[1]

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, the tumors should be classified as a fifth "subtype", namely "adenocarcinoma, mixed subtypes".[1]

Adenocarcinoma of the lung tends to stain mucin positive as it is derived from the mucus producing glands of the lungs. Similar to other adenocarcinoma, if this tumor is well differentiated (low grade) it will resemble the normal glandular structure. Poorly differentiated adenocarcinoma will not resemble the normal glands (high grade) and will be detected by seeing that they stain positive for mucin (which the glands produce).[12][13]

To reveal the adenocarcinomatous lineage of the solid variant, demonstration of intracellular mucin production may be performed. Foci of squamous metaplasia and dysplasia may be present in the epithelium proximal to adenocarcinomas, but these are not the precursor lesions for this tumor. Rather, the precursor of peripheral adenocarcinomas has been termed atypical adenomatous hyperplasia (AAH).[9] Microscopically, AAH is a well-demarcated focus of epithelial proliferation, containing cuboidal to low-columnar cells resembling Clara cells or type II pneumocytes.[9] These demonstrate various degrees of cytologic atypia, including hyperchromasia, pleomorphism, prominent nucleoli.[9] However, the atypia is not to the extent as seen in frank adenocarcinomas.[9] Lesions of AAH are monoclonal, and they share many of the molecular aberrations (like KRAS mutations) that are associated with adenocarcinomas.[9]

References[edit]

  1. ^ a b c d e f Travis, William D; Brambilla, Elisabeth; Müller-Hermelink, H Konrad; Harris, Curtis C, eds. (2004). Pathology and Genetics of Tumours of the Lung, Pleura, Thymus and Heart. World Health Organization Classification of Tumours. Lyon: IARC Press. ISBN 92-832-2418-3. Retrieved 27 March 2010. 
  2. ^ Smokers defined as current or former smoker of more than 1 year of duration. See image page in Commons for percentages in numbers. Reference:
  3. ^ Roggli VL, Vollmer RT, Greenberg SD, McGavran MH, Spjut HJ, Yesner R (June 1985). "Lung cancer heterogeneity: a blinded and randomized study of 100 consecutive cases". Hum. Pathol. 16 (6): 569–79. doi:10.1016/S0046-8177(85)80106-4. PMID 2987102. 
  4. ^ Rossi G, Marchioni A, Sartori1 G, Longo L, Piccinini S, Cavazza A (2007). "Histotype in non-small cell lung cancer therapy and staging: The emerging role of an old and underrated factor". Curr Resp Med Rev 3: 69–77. doi:10.2174/157339807779941820. 
  5. ^ Vincent MD (August 2009). "Optimizing the management of advanced non-small-cell lung cancer: a personal view". Curr Oncol 16 (4): 9–21. doi:10.3747/co.v16i4.465. PMC 2722061. PMID 19672420. 
  6. ^ a b c d Travis WD, Travis LB, Devesa SS (January 1995). "Lung cancer". Cancer 75 (1 Suppl): 191–202. doi:10.1002/1097-0142(19950101)75:1+<191::AID-CNCR2820751307>3.0.CO;2-Y. PMID 8000996. 
  7. ^ Subramanian J, Govindan R (February 2007). "Lung cancer in never smokers: a review". Journal of Clinical Oncology 25 (5): 561–70. doi:10.1200/JCO.2006.06.8015. PMID 17290066. 
  8. ^ 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.  edit
  9. ^ a b c d e f g h i j k l Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson. "Chapter 13, box on morphology of adenocarcinoma". Robbins Basic Pathology (8th ed.). Philadelphia: Saunders. ISBN 1-4160-2973-7. 
  10. ^ Goljan USMLE Audio Tapes, 2001
  11. ^ British Journal of Cancer (2004) 90, 646 – 651 T Marugame et al, Filter cigarette smoking and lung cancer risk; a hospital-based case–control study in Japan
  12. ^ Diseases of Lung
  13. ^ Adenocarcinoma of Lung (Mucin Stain)