Adenocarcinoma of the lung is one of the non-small cell carcinomas of the lung and is a malignant tumour with glandular differentiation or mucin production. This tumour exhibits various patterns and degrees of differentiation, including lepidic, acinar, papillary, micropapillary, and solid with mucin formation 1.
It is now considered the most common histological subtype in terms of prevalence.
Early symptoms are fatigue with mild dyspnoea followed by a chronic cough and haemoptysis at a later stage.
Lung adenocarcinoma is primarily categorized on the basis of histopathologic evaluation, although testing for genetic mutations (e.g. EGFR, KRAS) is becoming increasingly important for consideration of therapy 1.
Mucinous adenocarcinoma is recognized as distinct from non-mucinous adenocarinomas, given differences in imaging appearance, genetics, and clinical behavior.
Next, lung adenocarcinomas are divided into 'preinvasive', 'minimally invasive', and 'invasive' disease on the basis of greatest depth of invasion on on resection specimens (this assessment is not possible on limited biopsies) 1:
- preinvasive adenocarcinoma lesions: no invasion
- minimally invasive adenocarcinoma: ≤5 mm invasion
- invasive adenocarcinoma: >5 mm invasion
For invasive adenocarcinoma, further subcategorization is recommended according to the dominant histologic pattern. Both mucinous and non-mucinous adenocarcinomas typically consist of a mixture of histologic patterns (all previously known as "mixed subtype", a now defunct category), but reporting of the predominant subtype is specifically recommended for non-mucinous lesions 1:
- lepidic predominant adenocarcinoma of the lung: formerly non-mucinous bronchioloalveolar carcinoma (BAC) pattern, with > 5 mm invasion
- acinar predominant adenocarcinoma of the lung
- papillary predominant adenocarcinoma of the lung
- micropapillary predominant adenocarcinoma of the lung
- solid predominant with mucin
Variants of invasive adenocarcinoma:
- invasive mucinous adenocarcinoma (formerly mucinous BAC)
- fetal (low and high grade)
Sometimes it is impossible to radiographically distinguish between other histological lung cancer types.
A lung nodule is a rounded or irregular region of increased attenuation measuring less than 3 cm. The amount of attenuation can further classify the nodules as either ground glass, subsolid or solid.1,2
Histologically, the ground-glass attenuation corresponds to a lepidic growth pattern and the solid component corresponds to invasive patterns. Hence, the preinvasive category of adenocarcinoma in situ, minimally invasive adenocarcinoma, and the invasive subtype of lepidic-predominant adenocarcinoma are often seen as a ground-glass nodule or a subsolid nodule with a predominant ground-glass component. On the other hand, the remaining invasive subtypes of adenocarcinoma usually manifest as a solid nodule but may also be subsolid and are only occasionally seen as ground glass nodule 1,2.
The invasive mucinous adenocarcinoma subtype (formerly mucinous BAC) can have a variable appearance, including consolidation, air bronchograms, or multifocal subsolid nodules or masses 2.
Treatment and prognosis
There are society guideline recommendations for the imaging follow-up of both ground glass and solid nodules: Fleischner Society guidelines 3.
- 1. Travis WD, Brambilla E, Noguchi M et-al. International association for the study of lung cancer/american thoracic society/european respiratory society international multidisciplinary classification of lung adenocarcinoma. J Thorac Oncol. 2011;6 (2): 244-85. doi:10.1097/JTO.0b013e318206a221 - Pubmed citation
- 2. Austin JH, Garg K, Aberle D et-al. Radiologic implications of the 2011 classification of adenocarcinoma of the lung. Radiology. 2013;266 (1): 62-71. doi:10.1148/radiol.12120240 - Pubmed citation
- 3. MacMahon H, Naidich DP, Goo JM, Lee KS, Leung AN, Mayo JR, Mehta AC, Ohno Y, Powell CA, Prokop M, Rubin GD, Schaefer-Prokop CM, Travis WD, Van Schil PE, Bankier AA. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology. doi:10.1148/radiol.2017161659 - Pubmed
- 4. Aoki T, Tomoda Y, Watanabe H et-al. Peripheral lung adenocarcinoma: correlation of thin-section CT findings with histologic prognostic factors and survival. Radiology. 2001;220 (3): 803-9. Radiology (full text) - doi:10.1148/radiol.2203001701 - Pubmed citation
- 5. Lee SM, Goo JM, Park CM et-al. A new classification of adenocarcinoma: what the radiologists need to know. Diagn Interv Radiol. 2012;18 (6): 519-26. doi:10.4261/1305-3825.DIR.5778-12.1 - Pubmed citation
- 6.Blake Eric Christianson, Supriya Gupta, Shikhar G Vyas, Helena Spartz, Jayanth H Keshavamurthy. A diagnostic challenge: An incidental lung nodule in a 48-year-old nonsmoker. (2018) Lung India. 35 (3): 251. doi:10.4103/lungindia.lungindia_212_17 - Pubmed
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