When you are first diagnosed with lung cancer and a gene mutation such as EGFR or ALK is confirmed, you usually start taking a targeted therapy drug matched to it. Experiencing the tumor visibly shrink with a single pill is honestly somewhat reassuring. But this drug does not work forever. After a period as short as a few months or as long as a few years, the cancer cells find their own way to evade the drug. This is called "resistance."
Once the drug starts to stop working, the tumor begins to grow again on imaging or appears in new sites. At this point, the attending doctor often recommends, "Let's do another biopsy," and quite a few people are taken aback, asking why they have to do it again when they already did it once. That is entirely understandable. However, the repeat biopsy done here has a somewhat different purpose from the first diagnosis. It is meant to look into how the cancer has transformed itself to evade the drug — its "escape route."
In fact, in a considerable number of patients who were using a first-generation EGFR targeted therapy, a new mutation called T790M develops, and if this is confirmed, you can switch to a next-step drug that targets that mutation directly. In some cases, the lung cancer cells have even changed in nature to resemble small cell carcinoma. You have to know what has changed in this way in order to decide the next treatment without missteps. If a repeat biopsy is not done, you end up changing the drug based only on guesswork, so from the medical team's standpoint, they want to take one more look.
For those who find taking tissue again burdensome, a test done with blood, the so-called liquid biopsy, can be an alternative. It is a method of drawing blood and analyzing the gene fragments of cancer cells floating within it, and because there is no burden of piercing the lung with a needle, it is often tried first when the body's condition is poor or the tumor location is awkward. However, just because a mutation is not caught on the blood test does not mean it is absent, so when the result is ambiguous, things sometimes flow toward confirming it with a tissue biopsy after all. Which of the two is better differs from person to person, so it is decided by looking at the situation.
I hope you won't take the repeat biopsy itself too heavily. Rather than bad news, it is closer to gathering information to choose the next card. For things like the test method, risks, and whether anesthesia is involved, asking your medical team as questions come up is the most accurate.
This article is only general information to aid understanding, so please be sure to decide your own treatment direction in consultation with your attending physician.