How Long Does Chemotherapy Take To Work

Your oncologist has just finished explaining the chemotherapy regimen to you with a side effect list as long as the Nile. It looks like the cycles go on and on and on…

Plus he just said you have cancer in your liver, bones and lungs… and time may be short if the treatment doesn’t work.

You’re reeling from all this information he’s throwing at you. No one has told you any of this before.

Before you know it, he finishes up and gives you the hook:

‘Do you have any questions about what I’ve just said?’

‘Of course I have %#$% questions!’ You want to shout.

But you think to yourself… Do you even want to know?

And you hesitantly ask:

‘How long will the chemo take to work?’

Your oncologist looks uncertain for just a brief moment, but you catch it. Then he says something vague like ‘everyone is different, and every cancer is different. It’s difficult to say when or even if the cancer will shrink.’

And you’re shuffled out of his room to make way for the next patient.

I hope this didn’t happen to you but if it did, I’m sorry.

That’s so not a satisfying answer. I get it. It would be great if you could have some specifics here. It IS your life we’re talking about so casually.

How long does chemotherapy take to work?

The problem is he’s right. He was vague because there is no specific answer. It’s true, every cancer is different and every one is different. Ten patients with Stage 4 lung cancer will have ten different disease trajectories and responses to treatment. It drives oncologists crazy how much we still don’t know about cancer and how the individual will respond to treatment.

At the same time, we can give you general statistics with the caveat that these numbers are just what the studies show and is not specific to you.

Chemotherapy for Cancer

Chemotherapy is a common treatment for cancer, aimed at reducing the size of tumors and stopping the spread of cancer cells. The question of how long chemotherapy takes to shrink a tumor is complex (don’t you hate that word?). It depends on various factors including the type of cancer, the stage at which it’s diagnosed, and the specific chemotherapy drugs being used.

Understanding the timeline for chemotherapy and tumor shrinkage is crucial for setting realistic expectations and planning your treatment course so it’s great that you’re asking that question!

While each patient’s experience with chemotherapy is unique, knowing kinda-what-to-expect can help you prepare for the journey ahead.

Who does this question apply to?

Before I go on, I just want to make it clear that the question of ‘how long does chemo take to work?’ only applies to patients who are undergoing chemotherapy with the cancer still in their body. For example, when you have Stage IV cancer and surgery is not possible, or when you are undergoing neoadjuvant chemotherapy to shrink the tumor, making it easier for the surgeon to take it out.

If you have undergone surgery and there is no evidence of remaining cancer in your body, the aim of chemotherapy in your case is not to shrink the cancer, but to reduce the risk of the cancer ever coming back. Therefore, this question doesn’t apply to you.

The question you should be asking is: ‘What benefit in risk reduction can I expect from undergoing chemotherapy?’

Now let’s get back to this question:

The general response you can expect

Chemotherapy is a form of cancer treatment that works by targeting rapidly dividing cells, which is a common characteristic of cancerous growth. Chemotherapy drugs work by disrupting the cell cycle of cancer cells, preventing their replication and growth. Some drugs damage DNA directly, while others interrupt the cells’ division at various phases, leading to cell death.

In general, cancer treatment trials assess the response to chemotherapy with a scan (e.g CT scan, PET scan or MRI) every 2-3 months. Therefore, most oncologists will quote you a number along the lines of 2-3 months to see a response to chemotherapy. This is also why we wait 2-3 months before we arrange a scan to see if you have responded to treatment.

Are there other ways to know if I’m responding to chemotherapy?

Three months is a hell of a long time to suffer through chemo not knowing if you’ll respond to it. Is there a way to know earlier if you’re on the right track?

Of course! You don’t need a scan to tell you how well you’re doing. You’ll know by how you’re feeling. You’ll slowly start feeling better in yourself despite the chemotherapy side effects.

If your weight has been dropping off like nobody’s business, it will start to plateau. If you have cancer that is visible, for example, enlarged lymph nodes, or a tumor on the skin, you will see it stop growing and start shrinking.

And if your cancer was causing you pain, you will start seeing some relief.

If your blood tests were abnormal, for example, if your liver function was affected by cancer, the numbers will start to improve.

The progress of some cancers can be tracked by blood tumor markers:

• • prostate cancer can be tracked by PSA

• • ovarian cancer can be tracked by Ca-125

• • pancreatic cancer can be tracked by Ca 19-9.

• • bowel cancer cancer be tracked by CEA

Seeing some of these positive signs will help put your mind at ease that the chemotherapy is working and you’re on the right track.

Factors affecting tumor shrinkage

When you undergo chemotherapy, the time it takes for a tumor to shrink can be influenced by multiple factors:

• • Chemotherapy Regimen: Different drugs and combinations can lead to varying results.

• • Tumor Characteristics: Size, location, and growth rate are crucial. Some tumors may start to shrink after one round, but more commonly, it takes a few cycles.

• • Patient Health: Your overall health impacts how your body responds to chemotherapy.

Remember that each person’s case is unique. Your oncologist can provide a personalized estimate based on all these factors and more.

Chemo-sensitive cancers

Certain cancers that are very responsive to chemotherapy like small cell lung cancer and lymphomas will respond to chemotherapy treatment within weeks (one cycle). You don’t even need a scan to show you that you’re responding.

You’ll see your lymph nodes melting away in front of your eyes. It’s very satisfying, and you know for sure you’re on the right track.

Targeted Therapy

While this question pertains to response to chemotherapy, sometimes cancers are treated with targeted therapy. These biological agents are not chemotherapy but rather specific inhibitors for genetic mutations in the cancer.

They tend to work a lot quicker than chemotherapy, sometimes within weeks.

For example:

• • EGFR inhibitors like osimertinib for EGFR-mt lung cancer

• • BRAF and MEK inhibitors for metastatic melanoma

• • Trastuzumab for HER2+ breast cancer.

How long does immunotherapy take to work?

Immunotherapy is also commonly part of a combined regimen with chemotherapy now and is sometimes even administered by itself.

If immunotherapy was part of the treatment regimen with chemotherapy, you can expect the same answer of 2-3 months to respond.

However, if immunotherapy is given by itself, because of the way immunotherapy works, it can sometimes take a bit longer, up to 4-6 months to see any meaningful response.

In fact, sometimes immunotherapy can cause inflammation in the tumors, making it look temporarily larger. We call this ‘pseudo-progression’.

If my cancer doesn’t shrink in the first few months, will it shrink later?

I never like to say never. However, if your cancer doesn’t respond in the first few months to chemotherapy, it’s very unlikely it will respond later. More often than not, over time, the tumors will start to grow larger and we’ll need to switch treatments.

The caveat, as I discussed above, is when you’re on immunotherapy as well and may be experiencing pseudo-progression. Bear in mind that if you have new tumors popping up, it’s unlikely to be pseudo-progression but rather, true progression.

Sometimes, your cancer may be called ‘stable’. This means you’re feeling alright and on scans, your cancer has neither grown bigger nor shrunk. While I much prefer to see cancer shrink, when a cancer is stable, it’s still a sign that the chemotherapy is working.

I hope this article answered some of your pressing questions regarding response time to chemotherapy. If it didn’t, feel free to ask in the comments below.