Responses to glial cell line-derived neurotrophic factor change in mice as spermatogonial stem cells form progenitor spermatogonia which replicate and give rise to more differentiated progeny.

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis. These cells are classically defined as a subset of morphologically defined A single (As) spermatogonia, which can produce more SSCs or they can give rise to nonstem As cells that, upon replication, generate A paired (Apr) and then A aligned (Aal) spermatogonia. These latter two cell types, along with the nonstem As cells, function as transit-amplifying progenitor cells. It is known that glial cell line-derived neurotrophic factor (GDNF) is essential for maintaining all of these cells, but it is unknown if or how the responses of these cells change as they progress down the pathway to differentiated type A1 spermatogonia. We address this issue by using a chemical-genetic approach to inhibit GDNF signaling in vivo and an in vitro approach to increase GDNF stimulation. We show that inhibition for 2 days suppresses replication of As, Apr, and Aal spermatogonia to an equal extent, whereas stimulation by GDNF preferentially increases replication of As and Apr spermatogonia. We also test if inhibiting GDNF signaling causes As, Apr, and Aal spermatogonia to express Kit, an essential step in their differentiation into type A1 spermatogonia. Inhibition for 3 or 7 days produces a progressive increase in the percentages of As, Apr, and Aal undergoing differentiation, with the largest increase observed in Aal spermatogonia. Finally, we demonstrate that numbers of SSCs decrease more slowly than numbers of progenitor spermatogonia when GDNF signaling is inhibited. Taken together, these data suggest that there are significant changes in the responses to GDNF as SSCs give rise to progenitor spermatogonia, which replicate and gradually differentiate into type A1 spermatogonia.

Favourable long-term outcomes with brachytherapy-based regimens in men ≤60 years with clinically localized prostate cancer.

OBJECTIVE: To report long-term outcomes of men ≤60 years treated with brachytherapy (BT) for low- and intermediate-risk prostate cancer. PATIENTS AND METHODS: Of 1655 patients treated with BT for clinically localized prostate cancer between January 1998 and May 2008 at Memorial Sloan-Kettering Cancer Center, 236 patients with National Comprehensive Cancer Network low- (n = 178) or intermediate-risk (n = 58) prostate cancer were ≤60 years old with a 3-year minimum follow-up, and represent the subjects of this report. Brachytherapy was given either as monotherapy (n = 169) or with external beam radiation therapy (EBRT; n = 67). Forty-four patients (19%) received neoadjuvant cytoreductive hormone therapy. The 'nadir+2' definition was used for prostate-specific antigen (PSA) recurrence. Common Terminology Criteria for Acute Events (CTCAE) v 3.0 was used to grade genitourinary (GU) and gastrointestinal (GI) toxicity. Potency was defined as the ability to obtain an erection suitable for intercourse or an International Index of Erectile Function score ≥ 22. The Kaplan-Meier method and Cox regression were used for statistical analysis. The median follow-up was 83 months. RESULTS: The 8-year PSA relapse-free survival (RFS), cancer-specific and overall survival rates for the entire cohort were 96, 99 and 96%, respectively. For patients with low-risk disease, the 8-year PSA RFS rate was 97% and for intermediate-risk patients it was 94% (P = 0.34). There was no difference in PSA RFS between BT alone and combined therapy (P = 0.17). Late grade ≥ 2 GU and GI toxicity was 14 and 3%, respectively. Of 150 patients potent before treatment, 76 (51%) were potent at last follow-up, with 50/76 (66%) using no medication. There was no significant difference in post-treatment potency between BT alone and BT with EBRT (P = 0.74). CONCLUSIONS: Brachytherapy provides patients aged ≤ 60 years with low- and intermediate-risk prostate cancer with excellent outcomes and has a low risk of significant long-term GU or GI morbidity. Erectile function is preserved in >50% of patients and the majority do not require erectile dysfunction medication.

Improved clinical outcomes with high-dose image guided radiotherapy compared with non-IGRT for the treatment of clinically localized prostate cancer.

PURPOSE: To compare toxicity profiles and biochemical tumor control outcomes between patients treated with high-dose image-guided radiotherapy (IGRT) and high-dose intensity-modulated radiotherapy (IMRT) for clinically localized prostate cancer. MATERIALS AND METHODS: Between 2008 and 2009, 186 patients with prostate cancer were treated with IGRT to a dose of 86.4 Gy with daily correction of the target position based on kilovoltage imaging of implanted prostatic fiducial markers. This group of patients was retrospectively compared with a similar cohort of 190 patients who were treated between 2006 and 2007 with IMRT to the same prescription dose without, however, implanted fiducial markers in place (non-IGRT). The median follow-up time was 2.8 years (range, 2-6 years). RESULTS: A significant reduction in late urinary toxicity was observed for IGRT patients compared with the non-IGRT patients. The 3-year likelihood of grade 2 and higher urinary toxicity for the IGRT and non-IGRT cohorts were 10.4% and 20.0%, respectively (p = 0.02). Multivariate analysis identifying predictors for grade 2 or higher late urinary toxicity demonstrated that, in addition to the baseline Internatinoal Prostate Symptom Score, IGRT was associated with significantly less late urinary toxicity compared with non-IGRT. The incidence of grade 2 and higher rectal toxicity was low for both treatment groups (1.0% and 1.6%, respectively; p = 0.81). No differences in prostate-specific antigen relapse-free survival outcomes were observed for low- and intermediate-risk patients when treated with IGRT and non-IGRT. For high-risk patients, a significant improvement was observed at 3 years for patients treated with IGRT compared with non-IGRT. CONCLUSIONS: IGRT is associated with an improvement in biochemical tumor control among high-risk patients and a lower rate of late urinary toxicity compared with high-dose IMRT. These data suggest that, for definitive radiotherapy, the placement of fiducial markers and daily tracking of target positioning may represent the preferred mode of external-beam radiotherapy delivery for the treatment of prostate cancer.

Dose escalation for prostate cancer radiotherapy: predictors of long-term biochemical tumor control and distant metastases-free survival outcomes.

BACKGROUND: Higher radiation dose levels have been shown to be associated with improved tumor-control outcomes in localized prostate cancer (PCa) patients. OBJECTIVE: Identify predictors of biochemical tumor control and distant metastases-free survival (DMFS) outcomes for patients with clinically localized PCa treated with conformal external-beam radiotherapy (RT) as well as present an updated nomogram predicting long-term biochemical tumor control after RT. DESIGN, SETTING, AND PARTICIPANTS: This retrospective analysis comprised 2551 patients with clinical stages T1-T3 PCa. Median follow-up was 8 yr, extending >20 yr. INTERVENTION: Prescription doses ranged from 64.8 to 86.4 Gy. A total of 1249 patients (49%) were treated with neoadjuvant and concurrent androgen-deprivation therapy (ADT); median duration of ADT was 6 mo. MEASUREMENTS: A proportional hazards regression model predicting the probability of biochemical relapse and distant metastases after RT included pretreatment prostate-specific antigen (PSA) level, clinical stage, biopsy Gleason sum, ADT use, and radiation dose. A nomogram predicting the probability of biochemical relapse after RT was developed. RESULTS AND LIMITATIONS: Radiation dose was one of the important predictors of long-term biochemical tumor control. Dose levels < 70.2 Gy and 70.2-79.2 Gy were associated with 2.3- and 1.3-fold increased risks of PSA relapse compared with higher doses. Improved PSA relapse-free survival (PSA-RFS) outcomes with higher doses were observed for all risk groups. Use of ADT, especially for intermediate- and high-risk patients, was associated with significantly improved biochemical tumor-control outcomes. A nomogram predicting PSA-RFS was generated and was associated with a concordance index of 0.67. T stage, Gleason score, pretreatment PSA, ADT use, and higher radiation doses were also noted to be significant predictors of improved DMFS outcomes. CONCLUSIONS: Higher radiation dose levels were consistently associated with improved biochemical control outcomes and reduction in distant metastases. The use of short-course ADT in conjunction with RT improved long-term PSA-RFS and DMFS in intermediate- and high-risk patients; however, an overall survival advantage was not observed.