A Promising New Combination Therapy for a Rare, Hard-to-Treat Kidney Cancer

Fumarate hydratase-deficient renal cell carcinoma (FH-RCC) is an uncommon and fast-moving form of kidney cancer. It's driven by mutations in the FH gene, which disrupt a key step in cellular energy metabolism and appear to fuel aggressive tumor growth. Because it's rare, there's been no agreed-upon standard treatment, and patients have often been treated with approaches borrowed from more common kidney cancer types, with mixed results.

A new phase 2 clinical trial, published in Nature Communications, offers some encouraging early data on a combination approach: pairing the immunotherapy drug tislelizumab with the targeted therapy lenvatinib as a first-line treatment.

What the Trial Found

Researchers at Renji Hospital in Shanghai enrolled 20 patients with advanced FH-RCC and treated them with both drugs together. After following patients for a median of about 20 months, the results stood out for a cancer this difficult to manage. Nineteen out of 20 patients (95%) had their tumors shrink to a measurable degree, and every single patient saw their disease controlled to some extent, meaning no one experienced outright tumor progression as an initial response.

The typical patient went about 20.7 months before their cancer progressed, and among those who responded, the benefit lasted a median of roughly 19 months. Looking further out, an estimated 89.7% of patients were still alive two years after starting treatment. For context, FH-RCC has historically been associated with poor outcomes and rapid progression, so these numbers, while based on a small group, suggest this drug pairing may meaningfully change the treatment picture for at least some patients.

Weighing the Side Effects

No cancer therapy comes free of risk, and this combination was no exception. Nearly half of patients (45%) experienced a serious treatment-related side effect classified as grade 3 or higher, meaning it required active medical management. The paper describes this profile as "manageable," but that judgment reflects a clinical trial setting with close monitoring, and individual experiences with side effects can vary. Anyone considering this or a similar treatment path should talk through the specific risks and monitoring plan with their own oncology team.

Tracking Tumors Through the Blood

One of the more scientifically interesting parts of this study involved trying to monitor treatment response without repeated scans. Because FH-deficient tumors have a scrambled metabolism, they tend to produce unusual byproducts, including molecules called succinyl-adenosine and succinic-cysteine, that build up when the enzyme fumarate hydratase isn't working properly.

The research team measured these compounds in patients' blood over the course of treatment and compared the trends to what was showing up on imaging scans. In 80% of patients, the levels of these metabolites moved in step with tumor burden, rising when the cancer grew and falling when it shrank. That raises the possibility of a blood-based tool to help track how someone's cancer is responding between imaging appointments. It's an early finding, based on correlation rather than a validated diagnostic method, and the authors are clear that it needs further testing before it could be used in routine care.

What This Doesn't Tell Us Yet

The trial was conducted at a single center with only 20 participants and no comparison group receiving a different treatment. That design makes it hard to know for certain how this combination stacks up against other options, and results in a small group don't always hold up in larger, more diverse populations. The researchers themselves flag these limitations, and describe the findings as supportive of this combination as a "potential" first-line option rather than a settled answer.

Even so, for a cancer this rare and historically this difficult to treat, a 95% response rate in a prospective trial is a notable signal. Larger studies, ideally across multiple centers, would help confirm whether these results generalize and clarify exactly how the metabolic blood markers might fit into everyday patient monitoring.

Anyone diagnosed with FH-deficient RCC, or a related hereditary condition such as HLRCC, should discuss treatment options, clinical trial eligibility, and monitoring strategies with their own physician, since individual cases can differ substantially from those enrolled in a trial like this one.

Source: Nature Communications, DOI: 10.1038/s41467-026-77615-9, based on a phase 2 clinical trial led by Kong, Xu, Liu, and colleagues.