If my sister’s immunity is normal, how did she get cancer?

Question

Hello doctor,

My 35-year-old sister has been diagnosed with early-stage lung cancer after a CT scan revealed a small peripheral nodule. She had symptoms of a persistent dry cough and mild fatigue for a few months. She is a non-smoker and otherwise healthy.

Her tumor tested positive for an EGFR mutation, and her oncologist has started her on Osimertinib.

We are trying to better understand the role of the immune system in her case. Given her young age and overall good health, we assumed her immune system would be effective at preventing cancer from developing in the first place.

Her recent blood work, including NK cell count and T lymphocyte panel, was reported as within normal range. So our questions are:

If her immune system is functioning normally, how did the cancer develop?
Does the immune system fail to recognize cancer cells early on, or do cancer cells develop mechanisms to evade immune detection?
How does the concept of the tumor microenvironment contribute to this process, especially in otherwise healthy individuals?
Is there any evidence that improving or boosting immunity (through diet, supplements, or lifestyle changes) can meaningfully support treatment alongside targeted therapy like Osimertinib?

Also, she has no other comorbidities, and her LDH and CRP levels were only mildly elevated.

Please help.

Thank you.

Answer 1

Hello,

Welcome to icliniq.com.

I have read your query.

I understand why this feels confusing. When someone young and otherwise healthy develops cancer, the first instinct is to question whether something went wrong with the immune system. But that is usually not what is happening.

Your sister’s immune system is not weak. In fact, her reports suggest it is functioning normally. The issue is not about strength; it is about recognition and evasion.

Cancer cells come from our own bodies. In the early stages, they often look very similar to normal cells, so the immune system does not always identify them as a threat. Over time, some of these abnormal cells acquire the ability to hide or protect themselves. They can create a local environment around the tumor that essentially tells immune cells to stand down.

In her case, the EGFR (epidermal growth factor receptor) mutation is important. This type of lung cancer, which we often see in younger non-smokers, tends to grow more quietly. It does not provoke a strong immune reaction, so it can develop without being aggressively targeted by the body’s defenses.

This is why her blood tests can look completely normal, because the immune system overall is fine, but the tumor has found a way to avoid attention in its immediate surroundings. So this is not a failure of her body. It is a reflection of how clever cancer biology can be.

Regarding immunity and whether it can be boosted, this is a very common and understandable question. At present, we do not have good evidence that boosting the immune system with diet or supplements improves outcomes in this kind of lung cancer, especially when someone is already on a highly effective targeted treatment like Osimertinib.

What does help is much simpler and more important:

Maintaining good nutrition.
Avoiding unnecessary or high-dose supplements.
Staying consistent with treatment and follow-up.

Osimertinib is specifically designed to target cancers with EGFR (epidermal growth factor receptor) mutations, and it works in a very focused, effective way. That is where the real impact comes from.

I hope this answers your query.

Please let me know if I can assist you further.

Thank you.