The important value of prostate-specific antigen doubling time (PSADT). The value of prostate-specific antigen (PSA) in the early diagnosis of prostate cancer is well established and has been used to follow up patients with prostate cancer. The recent literature suggests that prostate-specific antigen doubling time (PSADT) may be valuable in the follow-up, treatment decision, efficacy evaluation and prognosis of prostate cancer patients. 1. Background of the emergence of PSADT If PSA values change linearly with time, then PSA velocity (prostate-specific antigen velocity, PSAV), i.e. PSA difference/time difference, can better characterize the PSA-time curve. However, it has been shown that the change of PSA value with time in prostate cancer patients is in the form of a power function rather than linear; log PSA only changes linearly with time when the logarithm of PSA value is taken (log PSA=a+bt). Mathematically speaking, a better indicator of the PSA-time curve characteristics at this time should be PSADT, which can be calculated by the following formula, PSADT = (log2)/k, k is the slope of the log PSA-time line. Just because PSADT can better characterize the PSA changes in real situations, it is more valuable in suggesting the patient’s condition and is getting more and more attention. 2, PSADT calculation When the PSA value changes as a power function of time, the PSADT can be calculated using two PSA values, PSADT = (t2-t1) log2 / (logPSA1-logPSA2), which is the simplest calculation method. However, when there are multiple PSA values, it is necessary to obtain the regression coefficient (b) by calculating the linear regression equation to obtain PSADT = (log2)/b. The PSADT value obtained by this method reflects the information including all PSA values and reduces the bias that may arise from the calculation through individual data. Recently, Svatek et al. applied the method of random coefficient model on this basis to reduce the bias caused by biological variation. The first two methods are the ones that are currently used more frequently. The first two PSA values after measurable blood PSA concentrations and all PSA values within 15 months were also used to calculate PSADT and compared in post-radical prostate cancer follow-up patients by Roberts et al. The results were found to be generally consistent. The PSADT was calculated using the early PSA values and the full PSA values and compared. Using early PSA values to calculate PSADT can help determine patients’ disease more easily and earlier so that timely interventions can be taken when necessary. The value of PSADT in the follow-up of prostate cancer patients Recent literature suggests that PSADT may be of great value in the prognostic judgment, efficacy evaluation and intervention decision of patients with prostate cancer follow-up, which is divided by treatment as follows. (1) Observational follow-up For patients with early stage prostate cancer with life expectancy <10 years and quality of life requirements, observational follow-up may be an option. If there is an indicator that can indicate the possibility of progression early, it is possible to intervene early to avoid losing the chance of cure. There is growing evidence that psadt may be an indicator of this. mclaren et al [5] found that psadt is a better indicator of disease progression than prostate cancer grading and staging in patients with early prostate cancer who are on observational follow-up, with almost half of patients with psadt <18 months progressing within 6 months. For patients with a short psadt, it is advisable to discontinue the observational follow-up and take active treatment measures. However, there is no unanimous opinion on the selection of an appropriate threshold value of psadt to guide clinical workup. Different authors have proposed different reference values, ranging from 24 months to 48 months [6-8]. Therefore, the selection of an appropriate reference value as a basis for clinical treatment decisions needs further research. (2) After radical prostate cancer surgery Predicting clinical recurrence An earlier study has pointed out the association between PSADT and tumor recurrence after radical prostate cancer surgery Patel et al [9] followed up 77 patients with elevated PSA after surgery and found that clinical recurrence was not found in 80% of patients with PSADT ≥ 6 months, while clinical recurrence was found in 36% of patients with PSADT < 6 months, and there was a significant difference between the two. There was a significant difference between the two. The PSA value is more stable and the PSADT is longer, while the PSADT is shorter when the prostate cancer recurs. Therefore, PSADT has been proposed to define biochemical recurrence (usually with postoperative PSA measurable or >0.2 ng/mL) to predict the possibility of clinical recurrence, but there is no definite PSADT reference value used to predict biochemical recurrence. Identifying the location of recurrence Identifying the location of recurrence can help to select the treatment plan, for example, radiotherapy is more effective in case of focal recurrence and endocrine therapy is chosen in case of distant metastasis, but early recurrence is often not detected by bone scan and MRI to help identify the site of recurrence. Recently, some studies have found that PSADT after biochemical recurrence may be related to the site of recurrence, thus facilitating early decision on salvage treatment options.Patel et al. reported that PSADT <6 months was most suggestive of distant metastasis, while focal recurrence had a relatively long PSADT. pound et al. found that patients had a higher likelihood of distant metastasis after surgery when PSADT ≤10 months, Gleason score >7, or PSA recurrence ≤2 years. Although there is not yet a PSADT value available to identify local recurrence and distant metastasis, these reports set the stage for further research. The role of salvage radiotherapy in the event of biochemical recurrence in patients with radical prostate cancer has not been established, but recently it has been suggested that the magnitude of PSADT may indicate the efficacy of salvage radiotherapy and provide assistance in the selection of appropriate cases for treatment.Numata et al. reported that those who responded to salvage radiotherapy (defined as PSA ≤0.1 ng/mL) had a mean PSADT of 6.2 months, whereas those who did not respond had a mean PSADT of 1.2 months. The difference was statistically significant, and those with PSADT ≥ 5 months had a better response to radiotherapy, so PSADT was used as an index to predict the efficacy of salvage radiotherapy, and it was considered that salvage radiotherapy was particularly effective when PSADT ≥ 5 months. The better outcome of salvage radiotherapy was mainly in cases of focal recurrence, suggesting that local recurrence is more likely in those with longer PSADT. Evaluation of patient prognosis A large sample size of studies have been conducted that correlate PSADT with long-term postoperative survival of patients.DAmico et al. The data of 1,451 patients with biochemical recurrence of prostate cancer after radical surgery or radiotherapy were analyzed, and it was found that the difference in prostate cancer specific mortality (PCSM) between those with PSADT <3 months and those with PSADT ≥3 months after either radical surgery or radiotherapy was statistically significant, and the relative hazard ratio of PCSM was 19.6. The relative risk ratio for PCSM was 19.6, with the former being nearly 20% higher than the latter. He used PSADT as a surrogate indicator to evaluate the prognosis of prostate cancer patients after radical surgery or radiotherapy. （As with radical prostate cancer, there is no definite conclusion that a certain PSADT value can be used to distinguish local recurrence from distant metastasis, but it has been studied by many authors. Hanlon et al. also confirmed that psadt was associated with distant metastasis after radiotherapy. Further studies are needed to inform clinical practice to identify the location of recurrence and to help decide whether to administer local therapy (e.g., cryotherapy) or endocrine therapy. Evaluating patient prognosis and aiding interventional decisions As previously mentioned, PSADT has been shown to correlate with patient prognosis after radiotherapy. Therefore, PSADT may be useful for early intervention in high-risk patients at the time of biochemical recurrence after radiotherapy. pinover et al. performed endocrine therapy or observed follow-up only in patients with biochemical recurrence (defined by ASTRO as 3 consecutive elevations of PSA) after radiotherapy, of which 148 patients had PSADT < 12 months, 59 accepted the recommendation for endocrine therapy and the remaining 89 refused. follow-up found The 5-year metastasis-free survival rate was higher in the former (78%/57%, P<0.01), but there was no difference in long-term tumor-specific survival; 100 patients with psadt ≥12 months, 89 accepted the recommendation for observational follow-up and the remaining 11 received deandrogenization therapy, and no significant difference was found in the 5-year metastasis-free survival rate. However, the study was retrospective, and a prospective randomized controlled clinical trial is needed to reveal whether early intervention in high-risk patients can improve long-term survival. < span=""> (4) Endocrine therapy Evaluation of patient prognosis Similarly, PSADT has been shown to correlate with the prognosis of patients treated with deandrogenation. hanlon et al. followed up patients treated with salvage endocrine therapy after radiotherapy and found that PSADT after endocrine therapy correlated with tumor-specific survival and overall survival of patients. Anticipated intervention effects PSADT may also be associated with endocrine therapy outcomes. Deferred anti-androgen therapy was used in 36 patients with hormone-non-dependent prostate cancer, all of whom had previously received only desandrogen therapy and were followed for PSA, but all eventually developed hormone-non-dependent prostate cancer. The PSADT was found to be a mean of 12.7 months for those with effective treatment and 7.5 months for those with ineffective treatment (P=0.037), finding that PSADT can help predict the efficacy of anti-androgen therapy and its duration. (5) Chemotherapy It has been suggested that PSADT may be an indicator to evaluate the prognosis of patients with hormone-non-dependent prostate cancer. Schmid et al. calculated PSADT in 40 patients with hormone-independent prostate cancer treated with chemotherapy and found that the mean PSADT was 7.9 months, 7.5 months and 3.8 months for patients in partial remission, stable disease and progressive disease, respectively, with significant differences, suggesting that PSADT may be an indicator of drug efficacy and duration. PSADT may be an adjunctive method for evaluating drug efficacy to compensate for the deficiency brought by the inability of bone scan to detect metastases at an early stage. PSADT has been of value in determining the prognosis, evaluating the efficacy and interventional decisions in the follow-up cases of prostate cancer, and is gaining more and more attention. Because of the convenience and affordability of PSA testing, it is reasonable to believe that PSADT will play a great role in clinical applications in the future as research on PSADT continues to improve.