An odds ratio of 2.55 for one common variant — several times anything on this site's other cancer pages. Testicular cancer is unusual twice over: it strikes young men, and its common genetics is unusually strong.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
Testicular germ cell tumour is the most common cancer in young men, and one of the most treatable — cure rates are high even when it has spread. It is also genetically strange in a way that is worth a page.
Most common cancer variants shift risk by five or ten per cent. The colorectal page on this site carries odds ratios of 1.06 and 1.09; prostate carries 1.15.
The chromosome 12 locus here has a per-allele odds ratio of 2.55 (95% CI 2.05–3.19, P = 10-31). That is a different order of thing: carrying two copies rather than none changes risk severalfold. The same study also found loci on chromosome 5 (OR 1.37) and chromosome 6 (OR 1.50) — both large by the usual standard, and both smaller than this one.
rs995030 sits near KITLG, which encodes the ligand for the receptor tyrosine kinase KIT. That pairing was already implicated in the biology of germ cells and in how these tumours arise, so the statistics and the biology point the same way — which is uncommon enough in this field to be worth noticing.
The study was not enormous by modern standards: 730 cases and 1,435 controls in the discovery scan, with 571 further cases and 1,806 controls for replication. It did not need to be. An effect this size shows up in samples that would miss an ordinary cancer variant entirely.
The study above, from 2010, found three loci. By 2017, two companion meta-analyses — the larger pooling 7,319 cases and 23,082 controls — had found dozens more, roughly doubling the number of known loci to 44. None of the new ones comes close to the chromosome 12 signal above; it remains the largest effect size found in the field, and that contrast is worth keeping rather than losing in the larger number.
What the expansion adds is convergence. Physical chromatin-interaction mapping (Hi-C, in testicular tumour cells) linked the 44 risk positions to candidate genes clustering around three themes: failed differentiation of the cells that would otherwise become sperm, defective assembly of the cell's internal scaffolding, and — the same pathway the original chromosome 12 locus sits in — disrupted KIT-MAPK signalling, including a newer variant near MAP2K1 itself, a step downstream of KIT. Together, the known loci now account for roughly a third of the excess risk a son inherits from his father; the original chromosome 12 signal remains the largest single piece of that by a wide margin.
Testicular cancer is uncommon, so several times a small risk is still a small risk. There is no screening programme for it and no guideline uses this genotype for anything.
What is worth knowing has nothing to do with DNA: a painless lump, swelling or a change in firmness of a testicle should be seen by a doctor promptly. Caught early or late, this cancer is usually curable — and the treatment is easier the earlier it starts. A history of undescended testis and a brother or father who has had it are the risk factors that clinicians actually use.
The study. Rapley et al. genotyped 307,666 SNPs in 730 cases and 1,435 controls from the UK, replicating in 571 further cases and 1,806 controls. Three susceptibility loci reached strong significance: chromosome 5 (per-allele OR 1.37, 95% CI 1.19–1.58, P = 3 x 10-13), chromosome 6 (OR 1.50, 95% CI 1.28–1.75, P = 10-13) and chromosome 12 (OR 2.55, 95% CI 2.05–3.19, P = 10-31). The chromosome 12 signal is attributed to KITLG, encoding the ligand for KIT, previously implicated in germ cell biology and in the pathogenesis of these tumours.
Why the effect is so large. Testicular germ cell tumour has one of the highest sibling relative risks of any cancer, and its common-variant architecture reflects that: several loci with odds ratios above 1.3 and this one above 2.5, against a background where most cancer GWAS hits sit near 1.1. Population incidence is low, so a large relative risk remains a small absolute one.
Clinical position. Diagnosis is clinical and radiological — examination, scrotal ultrasound, tumour markers (AFP, beta-hCG, LDH) — followed by orchidectomy for histology. Management is by stage and histological type, and cure rates are high including in metastatic disease. Established risk factors are cryptorchidism, a family history in a first-degree relative, and previous contralateral tumour. No genotype enters screening, diagnosis or treatment.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Testicular Germ Cell Tumour comes down to these specific, well-studied positions — not a diagnosis. 25 positions are linked to this page; the ones this page's own text discusses are shown first.
The studies behind these variants recruited participants from different ancestries — a result found in one population doesn't always transfer to another. Based on 25 of 25 linked studies with a resolved discovery ancestry.
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Testicular Germ Cell Tumour. MyGeneLog™. https://www.mygenelog.com/conditions/testicular-germ-cell-tumour
It is large for a common variant and still small in absolute terms, because the disease is uncommon to begin with. Several times a small number is a small number, and no screening or medical decision uses this.
Testicular germ cell tumour genuinely has a stronger common-variant architecture than most cancers — it also has one of the highest sibling relative risks. The study that found this needed only 730 cases, where an ordinary cancer variant needs tens of thousands.
Know that a painless lump or a change in a testicle is worth showing a doctor promptly, and that this cancer is usually curable. If your father or brother had it, or you had an undescended testis, say so — those are the risk factors clinicians act on.
Free to reuse. This page's text is original writing from freely-available research, licensed CC BY 4.0 — reuse it, including commercially, with attribution to MyGeneLog™. It's general research-derived information, not medical advice or a diagnosis — see Terms of Use.