The impact of the titanium cranial hardware in proton single-field uniform dose plans.

BACKGROUND: Neurosurgical cranial titanium mesh and screws are commonly encountered in postoperative radiation therapy. However, only a limited number of reports are available in the context of proton therapy, resulting in a lack of consensus among the proton centers regarding the protocol for handling the hardware. PURPOSE: This study is to examine the impact of the hardware in proton plans. The results serve as evidence for proton centers to generate standard operating procedures to manage the hardware in proton treatment. METHODS: Plans with different gantry angles and material overrides are generated on the CT images of a phantom made of the hardware. The dose distributions of the plans with and without material override, at different depths are compared. Films and ionization chambers are used to measure the plans and the measurements are compared to the treatment planning system (TPS) calculations by gamma analysis. RESULTS: There are some overdose and underdose regions downstream of the hardware. The overdose and underdose values are within a few percent of the prescribed dose when multiple fields with large hinge angles are used. The gamma analysis results show that the measurements agree with the TPS calculations within limits that are clinically relevant. CONCLUSION: The study has demonstrated the influence of the hardware on proton plans. Based on the result of this study, a standard operating procedure of managing the hardware has been implemented in our clinic.

Implementing and evaluating a high-resolution diode array for patient-specific quality assurance of robotic brain stereotactic radiosurgery/radiotherapy.

The purpose of the study was to introduce and evaluate a high-resolution diode array for patient-specific quality assurance (PSQA) of CyberKnife brain stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). Thirty-three intracranial plans were retrospectively delivered on the SRS MapCHECK using fixed cone, Iris, and multileaf collimator (MLC). The plans were selected to cover a range of sites from large tumor bed, single/multiple small brain metastases (METs) to trigeminal neuralgia. Fiducial tracking using the four fiducials embedded around the detector plane was used as image guidance. Results were analyzed before and after registration based on absolute dose gamma criterion of 1 mm distance-to-agreement and 0.5%-3% dose-difference. Overall, the gamma passing rates (1 mm and 3% criterion) before registration for all the patients were above 90% for all three treatment modalities (96.8 ± 3.5%, the lowest passing rate of 90.4%), and were improved after registration (99.3 ± 1.5%). When tighter criteria (1 mm and 2%) were applied, the gamma passing rates after registration for all the cases dropped to 97.3 ± 3.2%. For trigeminal neuralgia cases, we applied 1 mm and 0.5% criterion and the passing rates dropped from 100 ± 0.0% to 98.5 ± 2.0%. The mean delivery time was 33.4 ± 11.7 min, 24.0 ± 4.9 min, and 17.1 ± 2.6 min for the fixed cone, Iris, and MLC, respectively. With superior gamma passing rates and reasonable quality assurance (QA) time, we believe the SRS MapCHECK could be a good option for routine PSQA for CyberKnife SRS/SRT.

Pre-treatment factors associated with detecting additional brain metastases at stereotactic radiosurgery.

The number of brain metastases identified on diagnostic magnetic resonance imaging (MRI) is a key factor in consideration of stereotactic radiosurgery (SRS). However, additional lesions are often detected on high-resolution SRS-planning MRI. We investigated pre-treatment clinical characteristics that are associated with finding additional metastases at SRS. Patients treated with SRS for brain metastases between the years of 2009-2014 comprised the study cohort. All patients underwent frame-fixed, 1 mm thick MRI on the day of SRS. Patient, tumor, and treatment characteristics were analyzed for an association with increase in number of metastases identified on SRS-planning MRI. 289 consecutive SRS cases were analyzed. 725 metastases were identified on pre-treatment MRI and 1062 metastases were identified on SRS-planning MRI. An increase in the number of metastases occurred in 34 % of the cases. On univariate analysis, more than four metastases and the diameter of the largest lesion were significantly associated with an increase in number of metastases on SRS-planning MRI. When stratified by the diameter of the largest lesion into <2, 2-3, or ≥3 cm, additional metastases were identified in 37, 29, and 18 %, respectively. While this increase in the number of metastases is largely due to the difference in imaging technique, the number and size of the metastases were also associated with finding additional lesions. These clinical factors may be considered when determining treatment options for brain metastases.

Proton T2 measurement and quantification of lactate in brain tumors by MRS at 3 Tesla in vivo.

PURPOSE: To evaluate the T2 relaxation time of lactate (Lac) in brain tumors and the correlation of the T2 and concentration with tumor grades. METHODS: Eight pairs of the subecho time sets of point-resolved spectroscopy were selected between 58 and 268 ms, with numerical and phantom analyses, for Lac T2 measurement. In vivo spectra were acquired from 24 subjects with gliomas (13 low grade and 11 high grade) and analyzed with LCModel using numerically-calculated basis spectra. The metabolite T2 relaxation time was obtained from monoexponential fitting of the multi-echo time (TE) signal estimates versus TE. The metabolite concentration was estimated from the zero-TE extrapolation of the T2 fits. RESULTS: The Lac T2 was estimated to be approximately 240 ms, without a significant difference between low and high grade tumors. The Lac concentration was estimated to be 4.1 ± 3.4 and 7.0 ± 4.7 mM for low and high grades respectively, but the difference was not significant. CONCLUSION: The Lac T2 was similar among gliomas regardless of their tumor grades. This suggests that the T2 value from this study may be applicable to obtain the T2 relaxation-free estimates of Lac in a subset of brain tumors.

A retrospective analysis of tumor volumetric responses to five-fraction stereotactic radiotherapy for paragangliomas of the head and neck (glomus tumors).

BACKGROUND: Skull base paragangliomas (SBP) are locally expansile tumors that can be treated with stereotactic radiotherapy with favorable results. This report describes the results of 31 patients with SBP treated with CyberKnife radiotherapy delivering a total dose of 25 Gray in five fractions. METHODS: All patients treated with five-fraction CyberKnife radiotherapy at a single institution were identified between 2007 and 2013. Tumor volumetric analyses were performed to assess responses to radiotherapy. RESULTS: Median follow-up was 24 months with a range of 4-78 months. Local control and overall survival were 100%. Of the 20 patients who presented with tinnitus, 12 reported improvement (60%), of whom 6 reported complete resolution. There was a 37.3% reduction in tumor volume among all patients (p = 0.16). On subset analysis of patients with ≥24 months of follow-up, tumor volume decreased 49% (p = 0.01). The rate of grade 1-2 toxicity was 19%, with no grade 3 or worse toxicity. CONCLUSION: A five-fraction CyberKnife-based stereotactic radiotherapy approach is safe and efficacious for the management for patients with SBP. Our findings suggest the potential use of this strategy as a definitive or salvage treatment option for SBP.

PU.1 directly regulates cdk6 gene expression, linking the cell proliferation and differentiation programs in erythroid cells.

Cell proliferation and differentiation are highly coordinated processes during normal development. Most leukemia cells are blocked from undergoing terminal differentiation and also exhibit uncontrolled proliferation. Dysregulated expression of transcription factor PU.1 is strongly associated with Friend virus-induced erythroleukemia. PU.1 inhibits erythroid differentiation by binding to and inhibiting GATA-1. PU.1 also may be involved in controlling proliferation of erythroid cells. We reported previously that the G(1) phase-specific cyclin-dependent kinase 6 (CDK6) also blocks erythroid differentiation. We now report that PU.1 directly stimulates transcription of the cdk6 gene in both normal erythroid progenitors and erythroleukemia cells, as well as in macrophages. We propose that PU.1 coordinates proliferation and differentiation in immature erythroid cells by inhibiting the GATA-1-mediated gene expression program and also by regulating expression of genes that control progression through the G(1) phase of the cell cycle, the period during which the decision to differentiate is made.

Prior chemoradiotherapy adversely impacts outcomes of recurrent and second primary head and neck cancer treated with concurrent chemotherapy and reirradiation.

BACKGROUND: It has been shown that concomitant chemotherapy (C) with reirradiation (ReRT) is feasible and effective for select patients with recurrent or second primary head and neck cancer (HNC). To examine potential prognostic factors associated with survival, the authors of this report retrospectively reviewed the outcomes of patients who received CReRT. METHODS: The study cohort comprised previously irradiated patients with nonmetastatic disease from 9 consecutive phase 1 and 2 protocols for poor-prognosis HNC. For all patients, reirradiation (ReRT) was delivered with concurrent chemotherapy. Chemotherapy generally was 5-fluorouracil, hydroxyurea, and a third agent. RESULTS: One hundred sixty-six patients were identified, including 81 patients who underwent surgical resection or debulking before enrollment. The median ReRT dose was 66 gray. After a median follow-up of 53 months among surviving patients, the median overall survival (OS) was 10.3 months. The 2-year rates for OS, disease-free survival, locoregional control, and freedom from distant metastasis were 24.8%, 19.9%, 50.7%, and 61.4%, respectively. Thirty-three patients (19.9%) died of treatment-related toxicity. In subgroup analysis, survival was significantly reduced in patients who received previous concurrent chemoradiotherapy (CRT) compared with patients who were naive to CRT (2-year OS rate, 10.8% vs 28.4%; P = .0043). In multivariable analysis, prior CRT was associated independently with OS along with surgery before protocol treatment, full-dose ReRT, and radiotherapy interval. CONCLUSIONS: CReRT achieved a long-term cure for a small group of patients with recurrent or second primary HNC. Previous treatment with CRT was among the important prognostic factors for survival. Because of the associated risk of severe toxicity, CReRT should be limited only to carefully selected patients.

Radiotherapeutic strategies in the management of low-risk prostate cancer.

Prostate cancer is the most common nonskin malignancy among men in the United States. Since the introduction of screening with prostate-specific antigen (PSA), most patients are being diagnosed at an early stage with low-risk disease. For men with low-risk prostate cancer, there exists an array of radiotherapeutic strategies that are effective and well tolerated, such as external-beam radiotherapy and brachytherapy. In recent years, there have been tremendous advances in the field of radiation oncology that have transformed the way radiation is used to treat prostate cancer, such as intensity-modulated radiotherapy, image-guided radiotherapy, and stereotactic radiotherapy. It is now feasible to deliver high doses of radiation to the target volume with improved precision and spare more of the neighboring tissues from potentially damaging radiation. Disease outcomes are generally excellent in low-risk prostate cancer. Improvements are expected with further integration of innovative technologies in radiation delivery, tumor imaging, and target localization.

Improved outcomes after radiotherapy for prostate cancer: Anticoagulation, antiplatelet therapy, and platelet count as key factors in disease progression.

BACKGROUND: Several studies have suggested that antiplatelet (AP) or anticoagulant (AC) therapy may improve outcome in men with prostate cancer. We evaluated the effects of AP/AC therapy and tested the hypothesis that platelet count may also be associated with outcomes. METHODS: A total of 482 patients received primary radiotherapy (median dose 72 Gy) for nonmetastatic prostate cancer; 49% received androgen deprivation therapy. NCCN risk was low/intermediate/high risk in 39%/39%/22%. AP/AC therapy and platelet counts were analyzed with respect to freedom from biochemical failure (FFBF, nadir+2), distant metastasis (FFDM), and cause specific survival (CSS). RESULTS: After a median follow-up of 103 months, 10-year FFBF, FFDM, and CSS were 77%, 92%, and 96%, respectively. The 10-year cumulative incidence of BF and DM (with death as a competing event) was 19% and 7.0%, respectively. The 32% of men on AP/AC therapy had a lower incidence of 10-year BF (P = .016) and a trend toward a lower incidence of DM (P = .084) and CSS (P = .091). In the entire cohort, lowest platelet quartile (platelet count <187) was associated with higher 10-year BF (31% vs 16%, P = .0042) but not DM (9.4% vs 5.2%, P = .22) nor CSS (P = .76) compared with those patients with platelet count ≥187. AP/AC therapy was associated with a larger absolute reduction in BF for men with lowest platelet quartile (10-year BF of 21% vs 38%, P = .092) vs platelet ≥187 (10-year BF of 10% vs 18%, P = .053). Lowest platelet quartile remained associated with higher BF and DM on multivariable analysis controlling for risk category, WBC, and Hg. CONCLUSION: AP/AC was associated with improved FFBF. Low platelet count was associated with inferior FFBF and FFDM after prostate radiotherapy. This association was tempered when antiplatelet and anticoagulant therapy was administered.

Phase II trial of hippocampal-sparing whole brain irradiation with simultaneous integrated boost for metastatic cancer.

BACKGROUND: Advanced radiotherapeutic treatment techniques limit the cognitive morbidity associated with whole-brain radiotherapy (WBRT) for brain metastasis through avoidance of hippocampal structures. However, achieving durable intracranial control remains challenging. METHODS: We conducted a single-institution single-arm phase II trial of hippocampal-sparing whole brain irradiation with simultaneous integrated boost (HSIB-WBRT) to metastatic deposits in adult patients with brain metastasis. Radiation therapy consisted of intensity-modulated radiation therapy delivering 20 Gy in 10 fractions over 2-2.5 weeks to the whole brain with a simultaneous integrated boost of 40 Gy in 10 fractions to metastatic lesions. Hippocampal regions were limited to 16 Gy. Cognitive performance and cancer outcomes were evaluated. RESULTS: A total of 50 patients, median age 60 years (interquartile range, 54-65), were enrolled. Median progression-free survival was 2.9 months (95% CI: 1.5-4.0) and overall survival was 9 months. As expected, poor survival and end-of-life considerations resulted in a high exclusion rate from cognitive testing. Nevertheless, mean decline in Hopkins Verbal Learning Test-Revised delayed recall (HVLT-R DR) at 3 months after HSIB-WBRT was only 10.6% (95% CI: -36.5‒15.3%). Cumulative incidence of local and intracranial failure with death as a competing risk was 8.8% (95% CI: 2.7‒19.6%) and 21.3% (95% CI: 10.7‒34.2%) at 1 year, respectively. Three grade 3 toxicities consisting of nausea, vomiting, and necrosis or headache were observed in 3 patients. Scores on the Multidimensional Fatigue Inventory 20 remained stable for evaluable patients at 3 months. CONCLUSIONS: HVLT-R DR after HSIB-WBRT was significantly improved compared with historical outcomes in patients treated with traditional WBRT, while achieving intracranial control similar to patients treated with WBRT plus stereotactic radiosurgery (SRS). This technique can be considered in select patients with multiple brain metastases who cannot otherwise receive SRS.

Advances in radiotherapy for tumors involving the mediastinum.

RT is an integral component of treatment in many tumors of the mediastinum. In recent years, there have been advances in RT planning and delivery, which have allowed more effective radiation delivery while sparing normal tissues. New technologies and radiation modalities may help achieve disease control more safely and effectively.

PU.1 and pRB interact and cooperate to repress GATA-1 and block erythroid differentiation.

PU.1 and GATA-1 are two hematopoietic specific transcription factors that play key roles in development of the myeloid and erythroid lineages, respectively. The two proteins bind to one another and inhibit each other's function in transcriptional activation and promotion of their respective differentiation programs. This mutual antagonism may be an important aspect of lineage commitment decisions. PU.1 can also act as an oncoprotein since deregulated expression of PU.1 in erythroid precursors causes erythroleukemias in mice. Studies of cultured mouse erythroleukemia cell lines indicate that one aspect of PU.1 function in erythroleukemogenesis is its ability to block erythroid differentiation by repressing GATA-1 (N. Rekhtman, F. Radparvar, T. Evans, and A. I. Skoultchi, Genes Dev. 13:1398-1411, 1999). We have investigated the mechanism of PU.1-mediated repression of GATA-1. We report here that PU.1 binds to GATA-1 on DNA. We localized the repression activity of PU.1 to a small acidic N-terminal domain that interacts with the C pocket of pRB, a well-known transcriptional corepressor. Repression of GATA-1 by PU.1 requires pRB, and pRB colocalizes with PU.1 and GATA-1 at repressed GATA-1 target genes. PU.1 and pRB also cooperate to block erythroid differentiation. Our results suggest that one of the mechanisms by which PU.1 antagonizes GATA-1 is by binding to it at GATA-1 target genes and tethering to these sites a corepressor that blocks transcriptional activity and thereby erythroid differentiation.

Reversal of tumorigenicity and the block to differentiation in erythroleukemia cells by GATA-1.

Oncogenic transformation usually inhibits normal cell differentiation processes. Certain chemical agents can force some tumor cells to resume their differentiation program and undergo cell cycle arrest, an approach termed differentiation therapy. Mouse erythroleukemia (MEL) cells represent an important cell culture model system for investigating the principles of differentiation therapy. MEL cells are malignant erythroblasts that are blocked from differentiating into mature erythroid cells because of inappropriate expression of the transcription factor PU.1, which binds to and represses GATA-1, a key transcriptional stimulator of red blood cell differentiation. We report here that the block to differentiation in MEL cells can be overcome by providing the cells with additional GATA-1. A conditionally active form of GATA-1 can trigger the cells to differentiate, undergo terminal cell division, and lose their tumorigenicity. We also show that the gene for the cell cycle inhibitor p21 is transcriptionally regulated by GATA-1 and is a likely downstream effector of GATA-1 that helps to promote differentiation and proliferation arrest.

Aspirin improves outcome in high risk prostate cancer patients treated with radiation therapy.

PURPOSE: High-risk prostate cancer (PC) has poor outcomes due to therapeutic resistance to conventional treatments, which include prostatectomy, radiation, and hormone therapy. Previous studies suggest that anticoagulant (AC) use may improve treatment outcomes in PC patients. We hypothesized that AC therapy confers a freedom from biochemical failure (FFBF) and overall survival (OS) benefit when administered with radiotherapy in patients with high-risk PC. MATERIALS AND METHODS: Analysis was performed on 74 high-risk PC patients who were treated with radiotherapy from 2005 to 2008 at UT Southwestern. Of these patients, 43 were on AC including aspirin (95.6%), clopidogrel (17.8%), warfarin (20%), and multiple ACs (31.1%). Associations between AC use and FFBF, OS, distant metastasis, and toxicity were analyzed. RESULTS: Median follow-up was 56.6 mo for all patients. For patients taking any AC compared with no AC, there was improved FFBF at 5 years of 80% vs. 62% (P = 0.003), and for aspirin the FFBF was 84% vs. 65% (P = 0.008). Aspirin use was also associated with reduced rates of distant metastases at 5 years (12.2% vs. 26.7%, P = 0.039). On subset analysis of patients with Gleason score (GS) 9-10 histology, aspirin resulted in improved 5-year OS (88% vs. 37%, P = 0.032), which remained significant on multivariable analysis (P<0.05). CONCLUSIONS: AC use was associated with a FFBF benefit in high-risk PC which translated into an OS benefit in the highest risk PC patients with GS 9-10, who are most likely to experience mortality from PC. This hypothesis-generating result suggests AC use may represent an opportunity to augment current therapy.

Molecular pathways and potential therapeutic targets in glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the most common primary brain malignancy. The current standard of therapy consists of surgical resection followed by concurrent chemoradiotherapy with temozolomide. Despite steady advances in all therapeutic modalities, clinical improvements have been slow and the prognosis remains poor. Utilizing powerful large-scale molecular techniques, several key pathways implicated in gliomagenesis have recently been identified and confirmed. These represent potential therapeutic targets, and by developing novel methods to specifically manipulate these pathways, we may achieve a meaningful and substantial improvement in the way we treat GBM. Here, we present and discuss the current status of research into the molecular pathways and potential therapeutic targets in GBM.

Opportunities and challenges in the era of molecularly targeted agents and radiation therapy.

The first annual workshop for preclinical and clinical development of radiosensitizers took place at the National Cancer Institute on August 8-9, 2012. Radiotherapy is one of the most commonly applied and effective oncologic treatments for solid tumors. It is well recognized that improved clinical efficacy of radiotherapy would make a substantive impact in clinical practice and patient outcomes. Advances in genomic technologies and high-throughput drug discovery platforms have brought a revolution in cancer treatment by providing molecularly targeted agents for various cancers. Development of predictive biomarkers directed toward specific subsets of cancers has ushered in a new era of personalized therapeutics. The field of radiation oncology stands to gain substantial benefit from these advances given the concerted effort to integrate this progress into radiation therapy. This workshop brought together expert clinicians and scientists working in various disease sites to identify the exciting opportunities and expected challenges in the development of molecularly targeted agents in combination with radiation therapy.

ATM kinase inhibition preferentially sensitizes p53-mutant glioma to ionizing radiation.

PURPOSE: Glioblastoma multiforme (GBM) is the most lethal form of brain cancer with a median survival of only 12 to 15 months. Current standard treatment consists of surgery followed by chemoradiation. The poor survival of patients with GBM is due to aggressive tumor invasiveness, an inability to remove all tumor tissue, and an innate tumor chemo- and radioresistance. Ataxia-telangiectasia mutated (ATM) is an excellent target for radiosensitizing GBM because of its critical role in regulating the DNA damage response and p53, among other cellular processes. As a first step toward this goal, we recently showed that the novel ATM kinase inhibitor KU-60019 reduced migration, invasion, and growth, and potently radiosensitized human glioma cells in vitro. EXPERIMENTAL DESIGN: Using orthotopic xenograft models of GBM, we now show that KU-60019 is also an effective radiosensitizer in vivo. Human glioma cells expressing reporter genes for monitoring tumor growth and dispersal were grown intracranially, and KU-60019 was administered intratumorally by convection-enhanced delivery or osmotic pump. RESULTS: Our results show that the combined effect of KU-60019 and radiation significantly increased survival of mice 2- to 3-fold over controls. Importantly, we show that glioma with mutant p53 is much more sensitive to KU-60019 radiosensitization than genetically matched wild-type glioma. CONCLUSIONS: Taken together, our results suggest that an ATM kinase inhibitor may be an effective radiosensitizer and adjuvant therapy for patients with mutant p53 brain cancers.

Isolated central nervous system progression on Crizotinib: an Achilles heel of non-small cell lung cancer with EML4-ALK translocation?

Advanced non-small lung cancer (NSCLC) remains almost uniformly lethal with marginal long-term survival despite efforts to target specific oncogenic addiction pathways that may drive these tumors with small molecularly targeted agents and biologics. The EML4-ALK fusion gene encodes a chimeric tyrosine kinase that activates the Ras signaling pathway, and this fusion protein is found in approximately 5% of NSCLC. Targeting EML4-ALK with Crizotinib in this subset of NSCLC has documented therapeutic efficacy, but the vast majority of patients eventually develop recurrent disease that is often refractory to further treatments. We present the clinicopathologic features of three patients with metastatic NSCLC harboring the EML4-ALK translocation that developed isolated central nervous system (CNS) metastases in the presence of good disease control elsewhere in the body. These cases suggest a differential response of NSCLC to Crizotinib in the brain in comparison to other sites of disease, and are consistent with a previous report of poor CNS penetration of Crizotinib. Results of ongoing clinical trials will clarify whether the CNS is a major sanctuary site for EML4-ALK positive NSCLC being treated with Crizotinib. While understanding molecular mechanisms of resistance is critical to overcome therapeutic resistance, understanding physiologic mechanisms of resistance through analyzing anatomic patterns of failure may be equally crucial to improve long-term survival for patients with EML4-ALK translocation positive NSCLC.

Personalized Combined Modality Therapy for Locally Advanced Non-small Cell Lung Cancer.

Locally advanced non-small cell lung cancer (NSCLC) is a heterogeneous disease, and we have embarked on an era where patients will benefit from individualized therapeutic strategies based on identifiable molecular characteristics of the tumor. The landmark studies demonstrating the importance of molecular characterization of tumors for NSCLC patients, the promising molecular pathways, and the potential molecular targets/agents for treatment of this disease will be reviewed. Understanding these issues will aid in the development of rationally designed clinical trials, so as to determine best means of appropriately incorporating these molecular strategies, to the current standard of radiation and chemotherapy regimens, for the treatment of locally advanced NSCLC.

Aspirin use and the risk of prostate cancer mortality in men treated with prostatectomy or radiotherapy.

PURPOSE: Experimental evidence suggests that anticoagulants (ACs) may inhibit cancer growth and metastasis, but clinical data have been limited. We investigated whether use of ACs was associated with the risk of death from prostate cancer. PATIENTS AND METHODS: This study comprised 5,955 men in the Cancer of the Prostate Strategic Urologic Research Endeavor database with localized adenocarcinoma of the prostate treated with radical prostatectomy (RP) or radiotherapy (RT). Of them, 2,175 (37%) were receiving ACs (warfarin, clopidogrel, enoxaparin, and/or aspirin). The risk of prostate cancer-specific mortality (PCSM) was compared between the AC and non-AC groups. RESULTS: After a median follow-up of 70 months, risk of PCSM was significantly lower in the AC group compared with the non-AC group (3% v 8% at 10 years; P < .01). The risks of disease recurrence and bone metastasis were also significantly lower. In a subgroup analysis by clinical risk category, the reduction in PCSM was most prominent in patients with high-risk disease (4% v 19% at 10 years; P < .01). The benefit from AC was present across treatment modalities (RT or RP). Analysis by type of AC medication suggested that the PCSM reduction was primarily associated with aspirin. Multivariable analysis indicated that aspirin use was independently associated with a lower risk of PCSM (adjusted hazard ratio, 0.43; 95% CI, 0.21 to 0.87; P = .02). CONCLUSION: AC therapy, particularly aspirin, was associated with a reduced risk of PCSM in men treated with RT or RP for prostate cancer. The association was most prominent in patients with high-risk disease.