Revision 25 for 'Adenocarcinoma of the lung'

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Adenocarcinoma of the lung

Adenocarcinoma of the lung is one of the non-small cell carcinomas of the lung and is a malignant tumor with glandular differentiation or mucin production. This tumor exhibits various patterns and degrees of differentiation, including lepidic, acinar, papillary, micropapillary, and solid with mucin formation 1

Epidemiology

It is now considered the most common histological subtype in terms of prevalence.

Clinical presentation

Early symptoms are fatigue with mild dyspnea followed by a chronic cough and hemoptysis at a later stage.

Classification

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:

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:

 

Variants of invasive adenocarcinoma:

Radiographic features

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

Recommendation for follow-up of solid nodules is as per Fleischner Society guidelines. Please consult the 2017 Macmahon et al. article, Guidelines for management of incidental pulmonary nodules detected on CT images: from the Fleischner Society 2017 3.

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