{{Rsnum
|rsid=138213197
|Chromosome=17
|Orientation=plus
|geno1=(C;C)
|geno2=(C;T)
|geno3=(T;T)
|Gene=HOXB13
|position=48728343
|Gene_s=HOXB13
|Assembly=GRCh38
|GenomeBuild=38.1
|dbSNPBuild=141
}}[[rs138213197]], aka G84E, is a SNP in the homeobox transcription factor [[HOXB13]] gene located in a cluster of HOX genes on ch 17q21–22. This gene is a member of the abdominal B subfamily, which have posterior domains of expression, including in the vertebrate urogenital system. HOXB13 maintains a relatively high level of expression in the adult prostate. G84E consists of the non-conservative replacement of a glutamic acid for a glycine at this position in the HOXB13 protein.

In early 2012, findings were published based on exome sequencing of 200 genes spanning the ch17q21-22 region of primarily Caucasian [[prostate cancer]] patients (and matched controls). Deemed a "rare but recurring mutation", [[rs138213197]](T) was discovered and then validated in a larger case-case study. Overall, [[rs138213197]](T) was reported to lead to a 20-fold higher risk for [[prostate cancer]], based on having been observed in 72 of ~5,000 patients but in only 1 person out of 1400 controls (so overall odds ratio 20.1, CI: 3.5 - 803.3, p=8.5×10−7).{{PMID|22236224|OA=1
}}

Subsequent studies convincingly replicate this result:
** {{PMID|23104005|OA=1
}} Confirmed with odds ratio of 7.1 (CI: 4.62–10.78, p = 10e-19) based on 10,000 patients of various ethnicities (and ~60,000 controls).
** {{PMID|22841674}} Confirmed with odds ratio of 3.4 (CI: 2.2–5.4, p = 10e-6 or less) based on 5,000 Swedish patients. For this population, male G84E carriers have an estimated 33% cumulative risk to age 80 yr of prostate cancer, compared to 12% (CI: 11–13) among noncarriers. 
** {{PMID|22781434}} Confirmed with odds ratio of 5.8 (CI: 1.3 - 26.5, p = .01) based on 1,800 Canadian patients.
** {{PMID|23129385|OA=1
}} Confirmed with odds ratio of 3.3 (CI: 1.21 – 8.96) in 1,300 Caucasian men.
** {{PMID|22714738|OA=1
}} Confirmed with odds ratio of 7.9 (CI: 1.8 - 34.5, p = .0062) based on 928 Caucasian patients.
** {{PMID|22718278|OA=1
}} G84E not present in 671 Chinese patients or 1,536 controls, but a novel HOXB13 SNP, G135E found by sequencing in 3 of the cases (and no controls).

Is [[rs138213197]] also associated with breast cancer risk? Maybe, maybe not - it's too early to tell:
** {{PMID|23099437|OA=1
}} This study of 4,000+ Canadian and Polish patients indicates not; frequency of allele was 0.16%.
** {{PMID|22853031|OA=1
}} Of 877 patients, 6 women with BRCA1/2 wild-type, familial breast cancer (none Ashkenazi) Jewish ancestry had the variant, hence an odds ratio 5.7 (CI: 1-40, p=0.02).