Phosphaturic Mesenchymal Tumor, from the CureRays guide library.

Phosphaturic mesenchymal tumor is a rare, usually benign tumor that secretes a hormone (FGF23) and causes bone-softening 'tumor-induced osteomalacia'; complete surgical removal cures most cases and reverses the bone disease, with the FGF23-blocking drug burosumab and radiation reserved for tumors that can't be removed.

What it is.

Phosphaturic mesenchymal tumor (PMT) is a rare, usually small and slow-growing tumor of the soft tissue or bone. What makes it remarkable is not its size but a hormone it overproduces called FGF23. Excess FGF23 makes the kidneys waste phosphate into the urine, leading to low blood phosphate and a condition called tumor-induced osteomalacia — a softening of the bones that causes deep bone pain, muscle weakness, fatigue, and fractures, often for years before the tiny tumor is found. Because the tumor is frequently small and hidden (in a bone, foot, or deep tissue), specialized imaging such as a DOTATATE or octreotide scan is often needed to locate it. The good news is that PMT is almost always benign, and completely removing it cures the disease: FGF23 levels fall, blood phosphate normalizes, and the bone disease reverses, often dramatically. When a tumor cannot be found or safely removed, medicines and other local treatments can control the condition.

How radiation treats it.

Radiation damages the DNA inside tumor cells so they can no longer divide and function, while normal cells repair themselves more effectively. In phosphaturic mesenchymal tumor, surgery is the cure of choice; radiation is reserved for tumors that cannot be safely removed, where targeting the tumor can reduce its size and its overproduction of FGF23, helping the low-phosphate bone disease improve. Modern focused techniques concentrate the dose on the small tumor and spare nearby structures, and radiation is delivered as short, painless sessions that leave no radioactivity in your body.

The ways we can treat it.

Radiation for unresectable tumors. When a tumor cannot be surgically removed — for example, when it sits in a difficult or critical location — targeted radiation can shrink it or reduce its hormone output, helping control the bone disease.

Stereotactic / focused radiation. Precise high-dose radiation can treat a small, well-defined tumor in a hard-to-reach spot, or an isolated recurrence, while sparing surrounding tissue.

Image-guided ablation (alternative local therapy). Some small tumors can be destroyed with image-guided techniques such as radiofrequency or cryoablation when surgery is not ideal — chosen by the care team based on the tumor's location.

Questions we hear often.

Why did this small tumor make my bones hurt and weaken? The tumor overproduces a hormone called FGF23, which makes your kidneys lose phosphate into the urine. Low phosphate softens the bones (osteomalacia), causing deep bone pain, muscle weakness, and fractures. Removing the tumor reverses this.

Why was my tumor so hard to find? Phosphaturic mesenchymal tumors are often very small and can hide in a bone, foot, or deep tissue. Specialized scans such as a DOTATATE PET are used to locate them, after which surgery can cure the disease.

What if my tumor can't be removed? If the tumor can't be found or safely removed, medicines can control the condition — most notably burosumab, which blocks the FGF23 hormone, along with phosphate and active vitamin D. Targeted radiation or ablation may also be used to treat the tumor itself.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.