PET/CT uses a metabolically active tracer that allows clinicians to identify areas of the body that are hypermetabolic. Increased uptake of the tracer occurs in malignant cells and areas of inflammation or infection. Integrating the imaging reflective of metabolic activity with normal CT imaging allows for higher sensitivity and specificity compared to PET alone.MRI is reserved for patients with advanced disease where intracranial, or brain, involvement is likely. It is also helpful for evaluating the extent of chest wall, diaphragmatic, brachial plexus (such as in the case of superior sulcus tumors), or spine involvement. Histopathology
If possible, a biopsy of any suspected lung tumor is performed in order to make a microscopic evaluation of the cells involved and is ultimately required to confirm diagnosis. Biopsy should be attempted in distant lesions first to establish a histologic diagnosis and to simultaneously confirm metastatic staging. The biopsy material is also used to analyze whether the tumor express any specific mutations suitable for tageted therapy (e.g. EGFR mutation or ALK mutation). Biopsy can be accomplished via bronchoscopy, transthoracic needle biopsy, and video-assisted thorascopic surgery (VATS).While sputum cytology has been shown to have limited utility, thoracentesis, or aspiration of pleural fluid with an ultrasound-guided needle, should be performed when pleural effusion is present. When malignant cells are identified in the pleural aspirate of patients highly suspect for lung cancer, a definitive diagnosis and staging (stage IV adenocarcinoma of the lung) is established.Adenocarcinoma of the lung tends to stain mucin positive as it is derived from the mucus-producing glands of the lungs.
These subtypes are described below:

lepidic predominant 
acinar predominant 
papillary predominant 
micropapillary predominant 
solid predominant with mucin production Cell patterns identifying subtypes are associated with prognosis, ranging from favorable (lepidic) to intermediate (acinar and papillary) to poor (micropapillary and solid).Four discrete variants of invasive adenocarcinomas not assignable to these five subtypes are also included in the current classification:

invasive mucinous adenocarcinoma 
colloid adenocarcinoma 
fetal adenocarcinoma 
primary pulmonary enteric adenocarcinoma

Imaging
A chest x-ray (radiograph) is often the first imaging test performed when a person presents with cough or chest pain, particularly in the primary care setting. A chest radiograph may detect a lung nodule/mass that is suggestive of cancer, although sensitivity and specificity are limited.CT imaging provides better evaluation of the lungs, with higher sensitivity and specificity for lung cancer compared to chest radiograph (although still significant false positive rate). Computed tomography (CT) that is specifically aimed at evaluating lung cancer includes the chest and the upper abdomen. This allows for evaluation of other relevant anatomic structures such as nearby lymph nodes, adrenal glands, liver, and bones which may show evidence of metastatic spread of disease. Indeed, the US Preventative Services Task Force recommends annual screening with low-dose CT in adults aged 55 to 80 years who have a 30 pack-year smoking history and currently smoke or have quit within the past 15 years, with certain caveats (see Lung cancer screening).Nuclear medicine imaging, such as PET/CT and bone scan, may also be helpful to diagnose and detect metastatic disease elsewhere in the body.