The lungs are in contact with a very high volume of blood for every minute. As such, it is one of the most susceptible organs for metastasis. Cancer in the lungs is also very likely to spread, making lung cancer a particularly dangerous disease. Some cases are detected before spreading happens, while others have very accelerated growth and are only diagnosed when it is too late to take the primary tumor out.
Just like any other cancer, lung cancer starts as a bunch of cells that divide very rapidly. A tumor begins to grow from these cells, only limited to one area. As the cells divide more, they start undergoing mutations, making cancer more aggressive. In time, the tumor is not limited to a small area of the lung. It spreads locally, and the cells start traveling to distant locations.
Each of these steps in the process is described by cancer stages or grades. For therapeutics, it is imperative to know in which stage cancer is before planning what to do about it, and in this article, we will review how doctors stage lung cancer and what tools do they use.
Stages of Small-cell lung cancer & Stages of Non-Small-Cell lung cancer
Stages of Small-cell lung cancer
Small cell lung cancer only has two stages:
- Limited stage: It features cancer that is only found in one lung. No cancer cells are found in the other lung, and if any lymph nodes are taken, they are located on the same side of the affected lung. Only a minority of patients with SCLC are diagnosed with a limited-stage disease because it is rapidly-growing cancer often detected in a late stage.
- Extensive stage: It features cancer usually found in one lung, but we have either a secondary tumor in the other lung or any other organ. These patients may also have malignant tumors in the lymph nodes located on the other side of the chest. In patients with pericardial or pleural effusion, an extensive stage would have malignant cells on the liquid.
Stages of Non-Small-Cell lung cancer
We have 5 stages of non-small cell lung cancer. They are as follows:
- Stage 0: This is the earliest stage of cancer we can have. In this case, we have carcinoma in situ (cancer that is small and limited to its own space). No lymph node invasion and no metastasis is present.
- Stage I: In this stage, cancer is still very small (no more than 1 cm) or minimally invasive carcinoma (IA1). Another possibility is having a very small tumor of 1-2 cm (IA2) or 2-3 cm (IA3). If the tumor is larger than 3 cm but smaller than 4 cm, it is also stage I (IB). There’s no involvement of the lymph nodes in this stage, and there is no distant metastasis.
- Stage II: In this stage, we have larger cancer tumors, with 3 cm or more and lymph nodes taken but only located inside the affected lung. Still, no distant metastasis is found in this stage.
- Stage III: In this case, we have a 3-5 cm tumor with lymph nodes taken not only in the lungs but also in the mediastinal space, where the heart is enclosed. Another possibility is larger than 5 cm; it can also be stage III when no lymph nodes are taken outside of the affected lung (IIIA). When mediastinal lymph nodes are taken in a tumor larger than 5 cm or the opposite lung, and other lymph nodes outside of the lungs are taken, we’re in front of a IIIB stage.
- Stage IV: In this stage, it doesn’t matter how large the tumor is and how many lymph nodes are taken. We’re in front of a stage IV lung cancer if there is metastasis. It is further divided into stage IVA when metastasis is found in the pleural space, the contralateral lung, or in a single organ outside of the thorax. It is stage IVB when more than one organ outside of the thorax is taken by metastasis.
Useful Tests For Staging Lung Cancer
Staging is done by analyzing the results of different imaging tests and biopsies. The most common tests to stage lung cancer include:
- PET or PET-CT scans: Doctors use a PET scan to identify malignant lymph nodes and metastases around the lungs and other organs. PET and CT scans can be combined to gain more accuracy.
- High-resolution CT scans: They are performed instead of PET-CT scans if they are not available. However, there are certain limitations in a CT scan because they sometimes won’t distinguish benign from malignant lesions.
- MRI scans: This technique is instrumental in evaluating the vascular supply of the diaphragm and tumors near the lung’s apex. These are known as Pancoast tumors, and it is usually mesothelioma. The vasculature exam helps plan surgery and obtain insight into the behavior of this type of lung cancer.
- Blood tests: Alkaline phosphatase levels are higher in bone metastasis, and we can also find high levels of calcium in these cases. Other practical tests include a complete blood count, bilirubin, albumin, AST, ALT, and electrolytes. These are only made to see if the patient will tolerate treatment or to rule out the presence of a paraneoplastic syndrome.
- Biopsy: When there’s a questionable node, a suspicious nodule, or an uncertain diagnosis, biopsies can help figure out if there’s cancer or not.
- Brain imaging: They are usually MRI scans, but CT scans can also help detect neurologic abnormalities and possible metastasis in patients with headaches and other neurologic symptoms.
Prognosis according To The Stage
aggressive lung cancer tumor. The 5-year survival rate of patients in a limited stage is 20%. In the extensive stage, the 5-year survival rate is lower than 1%.
In non-small-cell lung cancer, the prognosis is more favorable. Patients in stage I have a 70% survival rate in 5 years. As the number of the stage increases, the survival rate is reduced, and it is also lower than 1% in the last stage of the disease.
References:
Sihoe, A. D., & Yim, A. P. (2004). Lung cancer staging. Journal of Surgical Research, 117(1), 92-106.
Detterbeck, F. C., Boffa, D. J., & Tanoue, L. T. (2009). The new lung cancer staging system. Chest, 136(1), 260-271.
Rami‐Porta, R., Asamura, H., Travis, W. D., & Rusch, V. W. (2017). Lung cancer—major changes in the American Joint Committee on Cancer eighth edition cancer staging manual. CA: a cancer journal for clinicians, 67(2), 138-155.
