The reason why lung cancer is so deadly, and so quick

It's important to know that lung cancer is cured in about 16-18% of patients, which is not a statistic to be proud of, but it's important to know that some patients are definitely cured of lung cancer, just not as many as anyone would hope.
 
Part of the challenge is that lung cancer is typically found when it is already stage 3 or stage 4 out of 4 stages, with staging being the measure of the extent of spread of the cancer in the body. The lower the stage, the more likely a person is to live for a long time (and in some cases, to be cured). Looking at "non-small cell lung cancer" (NSCLC), which represents about 88% of cancers in the US today, cures are achieved in about 70-75% of patients with stage 1 disease, 45-50% of those with stage 2 disease, about 20% of those with stage 3 disease, and they are vanishingly rare in patients with stage 4 NSCLC.  Up until very recently, our screening system for lung cancer included waiting until you had symptoms of the cancer, which most commonly occurs late in the disease, with high stage disease, and having little or no chance of cure. Most of the cures have historically been in patients who had an early stage cancer detected on imaging done when they went in for some other issue, such as a routine x-ray before a gallbladder surgery, etc. Screening, which is intended to be limited to those with higher risk for lung cancer (age 55-75 or 80 and with a significantly smoking history) markedly increases the chance of detecting a lung cancer when it's early and has a much better chance of being cured.
 
Another key point is that the biological behavior of a cancer varies from patient to patient. Lung cancer tends to be on the aggressive (relatively fast-growing) side in the pace at which it grows without treatment, but there is a wide range.  When detected as stage 4 (advanced, incurable) disease, if patients don't undergo treatment, the median survival of patients (the time at which half of patients have died and half remain alive) is about 4-5 months. However, some patients will have a cancer that grows and spreads at a pace that can kill them in a matter of days, while others will have a much slower-paced disease and can live a year or even years without treatment (a small minority can even have such indolent disease that they may never die from the cancer).
 
There is also a relatively high risk of invisible in addition to visible disease.  This is the main reason why the cure rate for even stage 1 disease in 75% and not 100%.  Surgery is potentially curative for early stage disease, and a combination of treatments (often chemo and radiation, or chemo with or without radiation followed by surgery) are potentially curative for stage III NSCLC, but lung cancer has a significant risk of having spread at a microscopic level --  in other words, there is a significant risk of invisible disease in addition to visible disease.  The best surgery and radiation won't treat microscopic disease that has spread distantly throughout the body. The higher the stage of the cancer, the higher the chance that the cancer has spread and isn't truly curable, even if it appears it might be.
 
Finally, there is the challenge of sensitivity vs. resistance of the cancer. Chemotherapy improves survival in the majority of patients, but lung cancer is not among the most responsive ones to systemic (whole body) treatment. Our chemo is more effective and less toxic than it was 10-20 years ago, by and large, and there are now several "targeted" systemic therapy approaches that can be very significantly beneficial for a minority of patients. That proportion of patients benefiting very significantly from a targeted therapy against a target identified on their cancer is growing but is still only in the 10-20% range. Overall, systemic therapy improves the median survival of patients with advanced/metastatic NSCLC by 3-4 months, at least, in the broad majority of patients, and a minority will live for more than 6-12 months, sometimes even several years, from highly effective systemic therapy, even if it isn't curative. We hope to see a growing proportion of patients living longer and longer from these treatments.  But advanced NSCLC essentially always becomes resistant to the therapies that are initially helpful.
 
I hope that helps answer your question. As is always the case for a big question, the answer isn't one factor but several converging issues.
Morever, as we know: 

• 40% of the cancer type across the world is lung cancer. The chief factor responsible for this cancer is smoking. Active as well as passive smoker both are affected by smoking. Depending upon the age factor cancer cells appear prominently. Smoking is not solely responsible. In some cases non smokers are badly affected due to extremes of pollution, food intake pattern, lifestyle, intake of carcinogenic and heredity. Symptoms of lung cancer are mostly seen at the third-A stage amidst many patients. However it may differ according to diversity in human body response. Apparently, stage 3-A and stage 3-B cancer patients survival rate of 5 years is only 2–15%. Rest patients are seen to have a survival rate of 2–3–4 years or even months. In the 4th stage the cancer might has already reached to some bones, affected one lung, lymph nodes and vocal cord.
• If your near and dear ones are affected by lung cancer, the best possible treatment you can give them is utmost care, love and motivation towards willingness to live happily:). Medical science is making improvements and advances in medications incessantly. You can assure expected longevity with proper medications. But with the ongoing treatment, co-operarion from the side of the patient is also of uber importance.
• Medications of ayurveda and healthy nutrient diet also proves miraculous in some patients health. It was seen rare though. But at least why not give it a try. Perhaps, you maybe lucky enough to get your disease cured. Here is the link which will be helpful for you :