Revision 33 for 'Adenocarcinoma of the lung'All Revisions
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.
It is now considered the most common histological subtype in terms of prevalence.
Early symptoms are fatigue with mild dyspnea followed by a chronic cough and hemoptysis 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 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.
FDG-PET/CT is nowadays an essential tool for the lung cancer staging, in particular, assessing for the nodal and distant metastatic disease
adenocarcinoma in situ, low-grade adenocarcinomas, and minimally invasive adenocarcinoma are commonly associated with PET false-negative results. Given resolution limitations, FDG PET/CT is recommended when assessing subsolid ground-glass lung lesions that have a solid component measuring more than 8 mm 7
PET/CT definition of the gross tumor volume is commonly smaller than on CT, in ~15% of patients 7, therefore the T component of the TNM staging must be measured on CT or updated by the pathological staging
blooming artifact usually makes PET/CT less reliable to assess chest wall or diaphragmatic invasion 7
Treatment and prognosis
There are society guideline recommendations for the imaging follow-up of both ground glass and solid nodules: Fleischner Society guidelines 3.