miR-371- A SENSITIVE MARKER FOR TESTICULAR CANCER

Orlando, Florida — Serum levels of microRNA-371a-3p (miR-371) appear to be a useful biomarker in testicular germ cell tumors (GCTs).

According to data presented here at the 2015 Genitourinary Cancers Symposium, miR-371 is a sensitive and specific biomarker that could outperform the classic markers currently used.

The researchers found that after treatment, all elevated levels of miR-371 returned to the normal range. And there was a correlation with tumor bulk; mean levels were significantly higher in patients with metastatic disease than in those with early-stage disease.

"MiR-371 is probably expressed in more than 90% of germ cell tumor patients. Notably, it is also expressed in seminoma, but unfortunately not in teratoma," said lead researcher Klaus-Peter Dieckmann, MD, from the Department of Urology at Albertinen-Krankenhaus Hamburg in Germany, who presented the findings. "It is specific for germ cell tumors, as shown by testicular vein examination," he said.

"The serum levels correlate with clinical stage, and there is a rapid decrease after treatment," he added.

The clinical management of GCTs is largely based on serum biomarker monitoring, Dr. Dieckmann explained. Markers currently used involve α-fetoprotein (AFP), β-human chorionic gonadotropin (bHCG), and lactate dehydrogenase. However, only 60% of all GCT patients have elevations of these markers. In particular, LDH has a low specificity.

"In seminoma, less than 20% express the bHCG," he said. "Clearly, there is an ongoing need for more and better biomarkers. The question is, can microRNAs be useful?"

MiR-371 Levels Coincide With Stage and Treatment

MiRNAs are small noncoding RNA molecules that are involved in several biologic processes that cover embryogenic development, cell differentiation, apoptosis, and tumorigenesis. They have attracted attention because of their potential use as biomarkers in various cancer types, and most of them are highly stable in body fluids.

To date, there are about 2000 known microRNAs, and they have been numbered for identification, he explained. "Numbers 371 to 373 have been found to be associated with germ cell tumors."

Pilot studies have indicated that miR-371 could be a feasible biomarker. Dr. Dieckmann and colleagues evaluated the usefulness of this marker in testicular cancer.

They collected serum samples from 84 consecutive patients with GCT (51 seminoma, 33 nonseminoma) and 86 healthy control subjects. In the GCT group, 67 patients had clinical stage I disease and 17 had systemic disease.

For the entire cohort, levels of miR-371 were evaluated before and after treatment. The researchers also measured miR levels in the testicular vein blood of 50 patients and in the tumor-surrounding hydrocele fluid in six patients.

Serum levels of miR-371 were measured with quantitative polymerase chain reaction, and quantified in relation to miR-20a, an internal standard.

Levels of miR-371 were higher in the majority of GCT patients (>90%), except those with teratoma, than in the control subjects. In addition, serum levels were higher in nonseminomas than in seminoma patients.

The researchers also addressed how quickly levels would decline after treatment. "A good tumor marker is supposed to correlate with tumor bulk and decrease with cancer remission," Dr. Dieckmann explained.

In patients with stage I disease, miR-371 levels dropped to the normal range after orchiectomy; in most cases, the levels dropped by 95% within 1 day.

For patients with metastasis, who had higher levels than the stage I patients to begin with (P = .05), levels decreased with each cycle of chemotherapy.

Specificity for Testicular Tumor

The researchers also looked at specificity. If elevated miRNA levels result from their secretion by the tumor, it would be expected that their local concentration in the serum of testicular vein blood would be higher than in the blood from a peripheral vein. In fact, in the cancer patients, levels were 210-fold higher in the testicular vein blood than in the peripheral blood, and 51-fold higher in the hydrocele fluid.

Serum levels of miR-371 appear to be a promising specific biomarker for GCTs, as suggested by the high serum levels in GCT patients, the rapid return of elevated levels to the normal range after treatment, the association between serum levels with tumor bulk, and the much higher levels of miR-371 in testicular vein blood, Dr. Dieckmann concluded.

Promising But More Work Needed

This is a promising new marker for GCT, particularly for early-stage patients who have normal levels of AFP and bHCG, said Darren R. Feldman, MD, from the Memorial Sloan Kettering Cancer Center in New York City.

But much work is needed before it is ready for routine clinical use, he cautioned.

"Evaluation is needed in more patients with advanced disease," Dr. Feldman said, and in more "high-risk stage I patients for detection of relapse."

Standardization, cost, and commercialization of the assay need to be addressed, he said, as does whether it should be used alone or in combination with other GCT miRNAs.

But issues aside, Dr. Feldman emphasized that further investigation is warranted.

The authors have disclosed no relevant financial relationships.

Genitourinary Cancers Symposium (GUCS) 2015: Abstract 376. Presented February 7, 2015.