Question: What is known about the Digit Ratio (2D:4D) cancer?

Context:
RESULTS: Right 2D:4D was not associated with TGCT [odds ratio (OR) for a one-standard deviation (SD) increase in right-hand 2D:4D: 1.12, 95% confidence interval (CI): 0.93-1.34]. The results were consistent when evaluating the association based on the left hand. The difference between right and left-hand 2D:4D was also not associated with TGCT risk [OR for a one-SD increase in ΔR-L: 1.03, 95% CI: 0.87-1.23]. 
Digit ratio (2D:4D) is associated with gastric cancer.
RESULTS: GCA group presented significantly higher left 2D:4D, but significantly lower R-L in comparison to healthy controls, particularly so for males. Digit ratio did not correlate to clinical staging or TNM staging.
The 2D:4D pattern found for gastric cancer parallels that earlier described for breast cancer.
Higher second fourth digit ratio predicts higher incidence of prostate cancer in prostate biopsy.
2D/4D ratio >0,95 (OR (CI 95%) 4,4 (1,491-13,107) was related to neoplasia. 
CONCLUSION: High digit ratio predicts PCa in men undergoing prostate biopsy. Digit ratio >0,95 has 4-fold risk of PCa compared to men with digit ratio ≤0.95.
RESULTS: African-American men with prostate cancer are 3.70 times more likely to have a low 2D:4D digit ratio than Caucasian men with prostate cancer (95% confidence interval: 1.98, 6.92; P < 0.0001). There were no statistically significant differences in the presence of metastasis, Gleason score, family history or age at diagnosis by digit ratio. CONCLUSION: 2D:4D ratio shows strong differences between African-Americans and Caucasians; however, it does not correlate with disease severity in men already diagnosed with prostate cancer. 
RESULTS: We found a direct association between left 2D:4D and breast cancer risk, an inverse association between Δ(r-l) and risk of breast cancer, but no association between right 2D:4D and breast cancer risk. Among breast cancer cases, both right 2D:4D and Δ(r-l) were inversely associated with age at diagnosis.
CONCLUSION: Digit ratio measures might be associated with breast cancer risk and age at onset of breast cancer.
Recent studies have reported a strong association between 2D:4D and risk of prostate cancer. 
RESULTS: No association was observed between 2D:4D and prostate cancer risk overall (HRs 1.00; 95% CIs, 0.92-1.08 for right, 0.93-1.08 for left). 
CONCLUSION: Our results are not consistent with an association between 2D:4D and overall prostate cancer risk, but we cannot exclude a weak inverse association between 2D:4D and early onset prostate cancer risk.
Males in the OSCC group presented significantly higher digit ratio (P = 0.03) in comparison with males with OPLs and individuals without oral lesions. CONCLUSIONS: According to the results, males with the higher digit ratio seem to be more prone to undergo malignization of lesions in the oral cavity. 
Compared with index finger shorter than ring finger (low 2D : 4D), men with index finger longer than ring finger (high 2D : 4D) showed a negative association, suggesting a protective effect with a 33% risk reduction (odds ratio (OR) 0.67, 95% confidence interval (CI) 0.57-0.80). Risk reduction was even greater (87%) in age group <60 (OR 0.13, 95% CI 0.09-0.21). CONCLUSION: Pattern of finger lengths may be a simple marker of prostate cancer risk, with length of 2D greater than 4D suggestive of lower risk.
In the case-control analysis (n = 263), after controlling for ethnicity, women who developed CIN were significantly more likely to have a higher 2D:4D compared with HPV-negative women. A similar, nonsignificant trend was observed among women with a persistent HPV infection. CONCLUSION: Lower fetal androgen exposure may predispose to persistent HPV and increased risk of CIN.
Low numbers of CAG repeats and low 2D:4D are both associated with high sperm numbers and protection against breast cancer. 
Digit ratio measures might be associated with breast cancer risk and age at onset of breast cancer.
A lower digit ratio is related to an increased detection rate of prostate cancer, a high percentage of core cancer volume and a high Gleason score.
 Digit ratio could act as a possible marker for cancer predisposition.
Right hand digit ratio (2D:4D) is associated with oral cancer.
CONCLUSION: Digit ratio measures might be associated with breast cancer risk and age at onset of breast cancer.
Second to fourth digit ratio: a predictor of prostate-specific antigen level and the presence of prostate cancer.
CONCLUSIONS: Patients with a lower digit ratio have higher risks of prostate biopsy and prostate cancer.
Second and fourth digit ratio has also found to be correlated with sexual orientation, left hand preference autism and some adult onset diseases such as breast cancer and myocardial infarction.
Low numbers of CAG repeats and low 2D:4D are both associated with high sperm numbers and protection against breast cancer.
Findings from AR studies predict that low 2D:4D will be associated with prostate and hepatocellular cancer, urolithiasis, ADHD, ankylosing spondylitis, spontaneous abortion, and polycystic ovaries, while high 2D:4D will be associated with motor neuron diseases and endometrial cancer.
We found a direct association between left 2D:4D and breast cancer risk, an inverse association between Δ(r-l) and risk of breast cancer, but no association between right 2D:4D and breast cancer risk
Digit ratio measures might be associated with breast cancer risk and age at onset of breast cancer
The 2D:4D pattern found for gastric cancer parallels that earlier described for breast cancer

Answer: Digit ratio (2D:4D) is associated with gastric cancer, prostate cancer, breast cancer, cervical intraepithelial neoplasia and oral squamous cell carcinoma. 2D:4D was found to be higher in patients diagnosed with gastric cancer and prostate cancer  patients relative to controls. Among prostate cancer patients, 2D:4D shows strong differences between African-Americans and Caucasians; however, it does not correlate with disease severity in men already diagnosed with prostate cancer. However, other authors did not find an association between 2D:4D  and prostate cancer risk.
 2D:4D is not associated with testicular germ cell tumors.