Radiopharm Theranostics Limited (RADX) shares absolutely exploded on Monday, jumping over 140% as traders piled in with volume hitting 21.33 million shares compared to the typical daily average of just 26,810 shares. That's not a typo—volume increased roughly 800-fold.

The catalyst? Interim data from the company's U.S. Phase 2b imaging trial that showed RAD 101, its experimental brain metastases imaging agent, hitting its primary endpoint in a big way.

Here's what happened. Radiopharm released results from the first twelve patients treated with RAD 101, a small-molecule imaging agent that targets fatty acid synthase (FASN) and gets radiolabelled with Fluorine-18. The technology, known as Pivalate, is designed to diagnose suspected recurrent brain metastases from solid tumors of various origins.

The interim analysis showed that 92% of patients—eleven out of twelve—achieved concordance with MRI, which was the trial's primary endpoint. In other words, when doctors used PET imaging with RAD 101, it matched up with what MRI scans were showing in brain metastases cases.

But there's more to it than just matching existing technology. The results demonstrated significant and selective tumor uptake in brain metastases, and importantly, the images confirmed metabolic activity in brain metastases even when MRI findings were equivocal or unclear. That's potentially a huge deal for oncologists trying to distinguish between actual recurrent disease and treatment effects.

"These compelling interim data significantly strengthen confidence in the success of our Phase II trial of RAD 101 and provide a strong foundation for initiating a pivotal study by the end of 2026," said Riccardo Canevari, CEO and managing director of Radiopharm Theranostics. He added that independent commercial assessments estimate RAD 101's U.S. market opportunity at more than $500 million annually, which could position it as one of the top three imaging agents in the market.

The company recently hit 50% patient enrollment in the Phase 2b trial, so there's still more data to come. RAD 101 has already received FDA Fast Track Designation to help distinguish recurrent disease from treatment effects in brain metastases originating from solid tumors, including leptomeningeal disease.

The market opportunity is substantial. In the U.S. alone, more than 300,000 patients are diagnosed annually with cerebral metastases, creating significant demand for better diagnostic tools.

Beyond RAD 101, Radiopharm is expanding its pipeline. In November, the company secured Australian approval to launch its First-In-Human Phase 1 clinical trial of RAD 402 for treating metastatic or locally advanced prostate cancer. RAD 402 is an anti-KLK3 monoclonal antibody radiolabelled with the radionuclide 161Tb.

Radiopharm Theranostics (RADX) shares closed up 141.31% at $10.27, approaching the stock's 52-week high of $11.00.