NET patient — and research advocate

In 2005, Ron Muhlenbruck of Osage, Iowa, went to the doctor with an odd, recurring problem: His face would become flushed as if he were experiencing a hot flash. He was prescribed metformin, a common diabetes medication, but over time he started seeing blood in his stools.  

His doctor “put some things together, and then did a urine test,” Muhlenbruck says.  

The test looked for 5-hydroxyindoleacetic acid (5-HIAA), a waste product from the liver’s breakdown of the hormone serotonin. Checking 5-HIAA levels in urine helps diagnose the presence of neuroendocrine tumors (NETs), which are cancers that form in cells that act like nerve cells and hormone-producing cells.

NETs are typically slow-growing tumors that most often occur in the small bowel, pancreas, and lungs. Early-stage tumor removal by surgery can be effective, but for many patients, diagnosis does not occur until a NET has been present for years and has spread to the other areas of the body. The slow growth of NETs also means that they don’t respond well to chemotherapies, which are effective in targeting fast-growing, highly proliferative cancer cells. 

While NETs are not common compared to other kinds of cancers, the number of people diagnosed with these cancers has risen more than fivefold since 1975.  

Muhlenbruck’s test for 5-HIAA came back positive, and he was referred to University of Iowa Health Care and its Holden Comprehensive Cancer Center, one of the country’s leading centers in NET research and treatment for the past 25 years. He enrolled in a clinical trial of a treatment known as peptide receptor radionuclide therapy, or PRRT, which binds to receptors on NET cells to kill the cells and slow tumor growth. This clinical trial established the safety of PRRT, which had already been approved in Europe, in the U.S.

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From 2005 to 2018, Muhlenbruck’s course of action was a combination of radiation, surgery, and the PRRT treatments he finished the day the treatment was approved by the FDA. Together, these approaches reduced the size of his tumors and slowed their growth. Muhlenbruck eventually served as a patient advocate as part of the UI’s first NET SPORE grant — joining international meetings that were held over Zoom so he could offer his input as someone who was treated through the advancements that resulted from research at Iowa. 

Now 79 years old, Muhlenbruck says that any side effects of his treatment have been “minor.” He was able to work until retirement and stay active. In 2024, his doctors discovered he had another type of tumor in his groin area, for which he is currently undergoing treatment at Holden Comprehensive Cancer Center at UI Health Care.  

Despite having a rare cancer for many years, “it was not a major thing in my day-to-day life,” Muhlenbruck says. “I’ve felt pretty good during the 20 years I’ve had this.”