Genes Linked to Drug Resistance in Testicular Cancer

Several new genetic mutations have been revealed that could drive testicular cancer. In addition, a gene has been identified, which may contribute to tumors becoming resistant to current treatments.

The main testicular germ cell tumor (TGCT) histologies are seminomas, which resemble undifferentiated primary germ cells, and non-seminomas, which show differing degrees of differentiation. Cure rates for TGCTs are generally high, due to the sensitivity of malignant testicular germ cells to platinum-based chemotherapies; however this is at the cost of an increased risk of metabolic syndrome, infertility and secondary cancer.

A team of scientists led by those at the Institute of Cancer Research (London, UK) used a genetic technique called whole-exome sequencing to examine tumor samples from 42 patients with undergoing testicular cancer treatment. Surgical specimens were snap frozen within 30 minutes of surgery and matched blood samples were collected at the time of surgery. Tumor samples were trimmed to remove surrounding normal tissue, and tumor cells were confirmed by histological assessment. Tumor and matched lymphocyte DNA were extracted by standard techniques.

Samples for whole-exome sequencing were quantified using Qubit technology (Invitrogen; Carlsbad, CA, USA) and sequencing libraries constructed from 50 ng of respective normal/tumor DNA. Library preparation was performed using 37 Mb Nextera Rapid Capture Exome kits (Illumina; San Diego, CA, USA), with enzymatic tagmentation, indexing polymerase chain reaction PCR, clean-up, pooling, target enrichment and post-capture PCR amplification/quality control performed in-house, following standardized protocols. Samples underwent paired-end sequencing using the Ilumina HiSeq2500 platform with a 100-bp read length.

The investigators uncovered a number of new chromosome duplications and other abnormalities that could contribute to the development of this cancer, as well as confirming a previous association with the V-Kit Hardy-Zuckerman 4 Feline Sarcoma Viral Oncogene Homolog gene (KIT). Their study also found defective copies of a DNA repair gene called X-Ray Repair Complementing Defective Repair In Chinese Hamster Cells 2 (XRCC2) in a patient who had become resistant to platinum-based chemotherapy. They were able to verify the link between XRCC2 and platinum resistance by sequencing an additional sample from another platinum-resistant tumor.

Clare Turnbull, MD, PhD, the team leader, said, “Our study is the largest comprehensive sequencing study of testicular tumors published to date, describing their mutational profile in greater detail than has been possible using previous technologies. We have identified new potential driver mutations for this type of cancer, and provided new evidence of a link between mutations in the gene XRCC2 and platinum treatment-resistant tumors.” The study was published on January 22, 2015, in the journal Nature Communications.

Related Links:
The Institute of Cancer Research
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Illumina