While skin cancer is still the most common form of cancer among men, prostate cancer is not far behind, unfortunately. Current statistics say that roughly 1 in 9 men will be diagnosed with prostate cancer during their lifetime. Though prostate cancer can be a serious disease, thankfully most men diagnosed with prostate cancer do not die from it. In fact, more than 2.9 million men in the United States who have been diagnosed with prostate cancer at some point are still alive today.

Still, there are about 10% of men for whom cancer cells do not remain localized to the primary site develop locally invasive and metastatic disease, which increases the severity of the disease and likelihood of death, while severely limiting treatment options. Now, investigators at the Yale University School of Medicine have uncovered a potential new biomarker that may identify patients at increased risk of prostate cancer metastasis. Findings from the new study were published recently in The American Journal of Pathology through an article titled “Syntaphilin Is a Novel Biphasic Biomarker of Aggressive Prostate Cancer and a Metastasis Predictor.”

“Predicting aggressive behavior in prostate cancer is an entirely unmet and urgent need,” noted senior study investigator Marie E. Robert, MD, professor in the department of pathology at Yale School of Medicine. “There are currently no tissue-based biomarkers to help clinicians reliably identify the subset of prostate cancer patients who will progress to life-threatening, disseminated disease and who would, therefore, benefit from systemic therapies before or following prostatectomy. If our findings are supported by larger studies, SNPH measurement in tumors could be developed into a predictive biomarker.”

In the current study, the researchers found that syntaphilin (SNPH)—a mitochondrial protein—is a key determinant of the balance between tumor cell proliferation and tumor cell invasion and is abundantly expressed in prostate cancer, where it exhibits high expression at the invasive tumor edge compared to the central tumor bulk, correlating with greater cell proliferation at the tumor edge location. The researchers also found that SNPH expression increases with increasing Gleason pattern. Of potential vital clinical relevance, low central tumor expression correlated with an increased risk of metastasis in a group of patients undergoing radical prostatectomy.

“We showed that SNPH, a molecule originally identified as a negative regulator of mitochondrial dynamics in neurons, is abundantly expressed in prostate cancer,” the authors wrote. “SNPH distribution in prostate cancer is spatially biphasic, with high expression at the invasive front, correlating with increased proliferative rates, as determined by Ki-67 labeling, and reduced levels in the central tumor bulk, which are further decreased in patients with distant metastases. Higher levels of SNPH were observed with increasing Gleason grade. Prostate tumors predominantly express a novel, extraneuronal isoform of SNPH that accumulates in mitochondria and maintains oxidative metabolism and tumor cell proliferation.”

The investigators analyzed tissue specimens from 89 men with prostate adenocarcinoma who had undergone removal of the prostate. They found that SNPH manifests a unique, biphasic spatial distribution in prostate tumors, meaning that in 96% of the prostate cancer tumors analyzed, SNPH levels were elevated at the outer invasive edge where it correlates with increased tumor cell proliferation but decreased within the central tumor core. This differential was more pronounced in more advanced tumors.

Interestingly, central tumor SNPH measures (H scores) were significantly lower in 16 patients with metastases compared to patients without metastases, whereas SNPH scores at the invasive edges were not different in patients with or without metastases. Most of the metastases also expressed SNPH strongly. The researchers suggest that SNPH acts as a negative regulator of mitochondrial activity and that its down-regulation in the central portions of primary prostate cancer is associated with an increased risk of metastatic disease.

“This is the first study to suggest a clinical role for SNPH assessment in prostate cancer prognosis, potentially confirming recent evidence in experimental models of its importance in the phenotypic switch between proliferative and metastatic tumor states,” Roberts concluded. “Our results also reaffirm a critical, emerging role of mitochondrial biology in influencing tumor behavior.”