Targeted serum miRNA (TSmiR) test for diagnosis and follow-up of (testicular) germ cell cancer patients: a proof of principle

Germ cell cancers (GCC) are the most frequent malignancy in young Caucasian males. GCC can consist of seminomas (SE) and non-seminomas (malignant NS: embryonal carcinoma (EC), yolk sac tumor (YS), choriocarcinoma (CH) and teratoma (TE)). Current serum-markers used for diagnosis and follow-up (AFP, hCG) are predominantly related to YS and CH and marker positivity can vary during disease. Therefore, stable markers consistently identifying more GCC components, specifically the stem cell components SE and EC, are of interest. Expression of the embryonic stem cell miR-371-3 and miR-302/367 clusters in SE/EC/YS suggest possible application of these micro-RNAs as GCC tumor-markers. The TSmiR protocol constitutes a complete, quality-controlled pipeline for the detection of miRs in serum, based on magnetic bead-based purification and qPCR quantification. As a proof of principle, TSmiR was applied to five independent serum sample series including 80 GCCs, 47 controls, 11 matched pre/post orchidectomy samples and 12 no-GCC testicular masses. GCC serum samples showed a consistent, significant (p < 0.0064) increase of miR-371/372/373/367 levels. Analogous, serum levels returned to baseline after orchidectomy (stage-I disease). Moreover, there was a trend toward higher miR levels in patients with metastasis. These results imply suitability for diagnosis and follow-up. TSmiR showed an overall sensitivity of 98%, clearly outperforming the traditional serum markers AFP/hCG (36%/57%, sensitivity(AFP) = 3%/45%; sensitivity(hCG) = 62%/66%, SE/NS). TSmiR misclassified one tumor as a control. Serum AFP/hCG and TSmiR combined identified all T samples correctly. In conclusion, TSmiR constitutes a highly sensitive and reproducible serum test for GCC patients, suitable to be prospectively tested for diagnostic and follow-up purposes.