Theranostics in Practice

Understanding Lutetium-177 PSMA Therapy for Prostate Cancer

An encouraging trend is emerging in clinical practice: good control of cancer, with very few side effects and a good quality of life, using a treatment called Lutetium-177 PSMA therapy. This is exactly the balance every cancer treatment aims for. Here is a simple look at how it works and why it is such a different way of treating cancer.

What Is Nuclear Theranostics?

Most cancer treatments are given because they have worked well for that type of cancer in general. The doctor expects the drug to find and act on the cancer, based on experience with similar patients, but cannot see this happening in any one individual beforehand.

Theranostics works differently. Before any treatment is given, doctors first take a special scan that shows exactly where the cancer is in that specific patient’s body and whether the treatment is actually likely to reach it. Only then is the treatment given.

A simple way to picture this is a lock and key. Cancer cells carry a particular “lock” on their surface; a marker not normally found elsewhere in the body. Scientists have designed a matching “key” that fits this lock very precisely. This same key is used twice, in two slightly different forms:

1. First, as a Scan:

   The key is attached to a tiny, safe amount of a tracer and injected into the body. Wherever it finds its matching lock, it lights up on a scan (called a PET/CT scan). This gives doctors a complete picture of exactly where the cancer is, all over the body.

2. Then, as Treatment:

   If the scan shows that the cancer lights up clearly, the same key is attached instead to a small dose of radiation and given as treatment. It travels straight to the cancer cells, the very same places the scan already showed, and delivers radiation directly to them, while sparing most of the healthy tissue around them.

In short, the scan acts like a rehearsal. It proves the treatment will go to the right place before a single dose is actually given. This also means treatment is only offered to patients whose own scan shows they are likely to benefit; something most other cancer treatments cannot offer in advance. This approach is already well-established for certain neuroendocrine tumours and thyroid cancers, and is now being used successfully in prostate cancer, with research expanding into several other cancers as well.

Lock and Key Model in Theranostics

Why Prostate Cancer Cells Are a Good Match

In prostate cancer, the “lock” on the cancer cell is called PSMA. Prostate cancer cells carry far more PSMA on their surface than normal cells do, often hundreds of times more, and this tends to increase the more advanced the cancer becomes. This makes PSMA an unusually reliable and specific target, which is exactly what makes this treatment possible.

What the Treatment Involves

1. A PSMA PET/CT scan first confirms that the cancer shows up clearly, all over the body, before treatment is planned.
2. The treatment itself is given as a simple drip into a vein, usually once every 6 weeks, for about 4 to 6 sessions depending on how well the cancer responds.
3. The radiation used travels only a very short distance, a few millimetres, so it acts mainly on the cancer cells themselves, with little effect on the healthy tissue nearby.
4. Blood tests and scans are repeated between sessions to check how well the cancer is responding and to decide how many sessions are needed.

Who Can Benefit, and Side Effects

A large international study (the VISION trial) showed that this treatment helped patients with advanced prostate cancer live significantly longer, particularly when other treatments had stopped working well. It is approved for use in advanced prostate cancer, often after other treatments such as hormone therapy or chemotherapy, and is now increasingly being used earlier in the course of the disease as well.

Compared to chemotherapy, this treatment is generally very well-tolerated. Most patients experience only mild tiredness, a temporary dry mouth or dry eyes, occasional mild nausea, and sometimes a temporary dip in blood counts, which is monitored with simple blood tests during treatment.

The Takeaway

If you or someone you know has prostate cancer, it is worth asking your doctor whether a PSMA PET scan may be useful: it can help with staging, understanding the cancer better, and planning the right treatment. If the scan shows that the cancer will respond well to this approach, Lu-PSMA therapy (now approved and used worldwide) offers a treatment that is generally gentle on the body while still being highly effective.

Theranostics is no longer a treatment of the future; it is here today, already changing how cancer is treated, and continuing to evolve.

If you have questions about whether a PSMA PET/CT scan or Lu-177 PSMA therapy may be right for you or a loved one, please feel free to reach out to the nuclear medicine department.

Dr. Arvind Arokia Rajan
Consultant & Clinical Lead Nuclear Medicine, PET CT & Theranostics
Kauvery Hospital, Chennai

Happy Doctors’ Day!