Highly Recurrent IDH1 Mutations in Prostate Cancer With Psammomatous Calcification

Prostate cancer is a heterogeneous disease with several well-recognized morphologic subtypes and histologic variants-subsets of which are enriched for or associated with specific genomic alterations. Herein, we report a cohort of 4 unique prostate cancers characterized by intratumoral psammomatous calcification-which we have termed prostate cancer with psammomatous calcification (PCWPC). Clinicopathologic review demonstrates that PCWPCs are high-grade (grade group ≥3) tumors that involve the anterior prostate, and integrative targeted next-generation sequencing reveals recurrent hotspot IDH1 mutations. This morphology-molecular correlation is independently confirmed in The Cancer Genome Atlas prostatic adenocarcinoma cohort, with 3 of the 5 IDH1-mutant prostate cancers showing psammomatous calcification (rφ = 0.67; Fisher exact test, P < .0001). Overall, these findings suggest that PCWPC represents a novel subtype of prostate cancer enriched for an anterior location and the presence of hotspot IDH1 mutations. Recognition of these unique morphologic features could help identify IDH1-mutant prostate cancer cases retrospectively and prospectively-facilitating future large research studies and enabling clinical trial enrollment and precision medicine approaches for patients with advanced and/or aggressive disease.

Serial Molecular Profiling of Low-grade Prostate Cancer to Assess Tumor Upgrading: A Longitudinal Cohort Study

BACKGROUND

The potential for low-grade (grade group 1 [GG1]) prostate cancer (PCa) to progress to high-grade disease remains unclear.

OBJECTIVE

To interrogate the molecular and biological features of low-grade PCa serially over time.

DESIGN, SETTING, AND PARTICIPANTS

Nested longitudinal cohort study in an academic active surveillance (AS) program. Men were on AS for GG1 PCa from 2012 to 2017.

INTERVENTION

Electronic tracking and resampling of PCa using magnetic resonance imaging/ultrasound fusion biopsy.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

ERG immunohistochemistry (IHC) and targeted DNA/RNA next-generation sequencing were performed on initial and repeat biopsies. Tumor clonality was assessed. Molecular data were compared between men who upgraded and those who did not upgrade to GG ≥ 2 cancer.

RESULTS AND LIMITATIONS

Sixty-six men with median age 64 yr (interquartile range [IQR], 59-69) and prostate-specific antigen 4.9 ng/mL (IQR, 3.3-6.4) underwent repeat sampling of a tracked tumor focus (median interval, 11 mo; IQR, 6-13). IHC-based ERG fusion status was concordant at initial and repeat biopsies in 63 men (95% vs expected 50%, p <  0.001), and RNAseq-based fusion and isoform expression were concordant in nine of 13 (69%) ERG⁺ patients, supporting focal resampling. Among 15 men who upgraded with complete data at both time points, integrated DNA/RNAseq analysis provided evidence of shared clonality in at least five cases. Such cases could reflect initial undersampling, but also support the possibility of clonal temporal progression of low-grade cancer. Our assessment was limited by sample size and use of targeted sequencing.

CONCLUSIONS

Repeat molecular assessment of low-grade tumors suggests that clonal progression could be one mechanism of upgrading. These data underscore the importance of serial tumor assessment in men pursuing AS of low-grade PCa.

PATIENT SUMMARY

We performed targeted rebiopsy and molecular testing of low-grade tumors on active surveillance. Our findings highlight the importance of periodic biopsy as a component of monitoring for cancer upgrading during surveillance.

Biologic Significance of Magnetic Resonance Imaging Invisibility in Localized Prostate Cancer

PURPOSE

Multiparametric magnetic resonance imaging (mpMRI) is used widely for prostate cancer (PCa) evaluation. Approximately 35% of aggressive tumors, however, are not visible on mpMRI. We sought to identify the molecular alterations associated with mpMRI-invisible tumors and determine whether mpMRI visibility is associated with PCa prognosis.

METHODS

Discovery and validation cohorts included patients who underwent mpMRI before radical prostatectomy and were found to harbor both mpMRI-visible (Prostate Imaging and Reporting Data System 3 to 5) and -invisible (Prostate Imaging and Reporting Data System 1 or 2) foci on surgical pathology. Next-generation sequencing was performed to determine differential gene expression between mpMRI-visible and -invisible foci. A genetic signature for tumor mpMRI visibility was derived in the discovery cohort and assessed in an independent validation cohort. Its association with long-term oncologic outcomes was evaluated in a separate testing cohort.

RESULTS

The discovery cohort included 10 patients with 26 distinct PCa foci on surgical pathology, of which 12 (46%) were visible and 14 (54%) were invisible on preoperative mpMRI. Next-generation sequencing detected prioritized genetic mutations in 14 (54%) tumor foci (n = 8 mpMRI visible, n = 6 mpMRI invisible). A nine-gene signature (composed largely of cell organization/structure genes) associated with mpMRI visibility was derived (area under the curve = 0.89), and the signature predicted MRI visibility with 75% sensitivity and 100% specificity (area under the curve = 0.88) in the validation cohort. In the testing cohort (n = 375, median follow-up 8 years) there was no significant difference in biochemical recurrence, distant metastasis, or cancer-specific mortality in patients with predicted mpMRI-visible versus -invisible tumors (all P > .05).

CONCLUSION

Compared with mpMRI-invisible disease, mpMRI-visible tumors are associated with underexpression of cellular organization genes. mpMRI visibility does not seem to be predictive of long-term cancer outcomes, highlighting the need for biopsy strategies that detect mpMRI-invisible tumors.

Radiogenomic characterization of multifocal prostate cancer

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Background: Up to 20% of patients with negative multiparametric magnetic resonance imaging (MRI) harbor Gleason score ≥7 prostate cancer (PCa). We sought to elucidate the molecular basis of and determine the prognostic significance of PCa visibility on MRI. Methods: We identified a retrospective cohort of patients who underwent MRI prior to prostatectomy with both MRI visible (PIRADS 3 – 5) and invisible PCa. MRI for each patient was re-reviewed and co-registered with whole-mount histopathology. DNA and RNA were co-isolated from all tumor foci pre-identified on FFPE specimens. High depth, targeted DNA and RNA next generation sequencing was performed to characterize the molecular profile of each tumor focus using the Oncomine Comprehensive Panel (DNA) and a custom targeted RNAseq panel assessing PCa relevant alterations. A multigene RNAseq model was developed and validated in two independent cohorts to predict MRI visible PCa and to determine the prognostic significance of MRI visibility. Results: A total of 26 primary tumor foci from 10 patients were analyzed. Of the 14 (54%) invisible lesions on MRI, 5 (36%) were Gleason 3+4 = 7 and the remainder were Gleason 6. We detected high-confidence prioritized PCa relevant mutations in 54% (14/26) of tumor foci, 43% (6/14) of which were in MRI invisible lesions. Notable point mutations were in APC, AR, ARID1B, ATM, ATRX, BRCA2, FAT1, MAP3K1, NF1, SPEN, SPOP, and TP53. A 9-gene RNA signature, the majority of which were under-expressed cellular organization and structure genes, was developed to predict MRI visibility with an AUC of 0.89. Validation of this signature in an independent data set (n = 16) yielded an AUC of 0.88 with a specificity of 100% for predicting MRI visible tumors. Using this signature in a cohort of 375 patients with clinical follow up, we found that predicted MRI visibility status was not an independent predictor of biochemical recurrence, metastasis-free survival, or PCa specific mortality (all p > 0.05). Conclusions: We observed under-expression of cellular organization and structural genes in MRI visible tumors compared to MRI invisible cancer foci. Using our validated signature to predict MRI visibility status, we found that MRI visibility is not a significant predictor of oncological outcomes.

Molecular characterization of longitudinally tracked prostate cancer foci in men on active surveillance for low-risk disease

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Background: The biological trajectory of Gleason score 6 (GS6) prostate cancer (PCa) in men on active surveillance (AS) is unknown. We herein evaluate the potential for high grade PCa to arise clonally from GS 6 disease and determine the capacity of tissue-based biomarkers to predict grade progression. Methods: Men on AS with GS6 PCa who underwent magnetic resonance imaging/ultrasound (MRI/US) fusion biopsy on two occasions from 2012 through 2017 were enrolled. Tumor foci were tracked and re-sampled using the MRI/US fusion biopsy platform. ERG immunohistochemistry (IHC) and DNA/RNA next generation sequencing (NGS) were performed on formalin-fixed paraffin-embedded (FFPE) initial and repeat biopsy specimens to assess tumor clonality and evaluate candidate molecular markers of PCa grade progression. Results: Sixty-seven men of median age 64 years (IQR 59-69) and PSA 4.9 ng/ml (IQR 3.3-6.4) underwent repeat sampling of a single tracked tumor focus using MRI/US fusion biopsy. The median interval to repeat biopsy was 11 months (IQR 6-13). On repeat biopsy, 31 (46%) men progressed to high-grade (GS≥7) disease (n = 24, GS 3+4 = 7; n = 7, GS ≥4+3 = 7). Among the 67 subjects, ERG IHC status was concordant between initial and repeat biopsy in 64 (96%). Of 134 total specimens obtained (67 initial + 67 repeat biopsies), ERG status determined by NGS was concordant with ERG status by IHC in 132 (99%). Comparing the initial biopsy specimens in men who did versus did not undergo grade progression on follow up biopsy, derived cell cycle progression (CCP) scores (median 57.3 vs. 44.0, p = 0.11) and genomic prostate scores (GPS; median 73.8 vs. 64.4, p = 0.15) were not significantly different. Similarly, expression of FOLH1, PCAT4, SCHLAP1, and SPINK1 on initial biopsy did not significantly differ among men who did and did not undergo grade progression. Conclusions: Use of MRI/US fusion biopsy facilitated resampling of the same clonal focus of cancer over time, with high concordance of ERG status determined by both IHC and NGS. Derived genomic classifiers and candidate individual gene expression markers measured on initial biopsy tissue were not significantly different between patients who progressed and those who did not.

Transcriptomic heterogeneity in multifocal prostate cancer

BACKGROUND

Commercial gene expression assays are guiding clinical decision making in patients with prostate cancer, particularly when considering active surveillance. Given heterogeneity and multifocality of primary prostate cancer, such assays should ideally be robust to the coexistence of unsampled higher grade disease elsewhere in the prostate in order to have clinical utility. Herein, we comprehensively evaluated transcriptomic profiles of primary multifocal prostate cancer to assess robustness to clinically relevant multifocality.

METHODS

We designed a comprehensive, multiplexed targeted RNA-sequencing assay capable of assessing multiple transcriptional classes and deriving commercially available prognostic signatures, including the Myriad Prolaris Cell Cycle Progression score, the Oncotype DX Genomic Prostate Score, and the GenomeDX Decipher Genomic Classifier. We applied this assay to a retrospective, multi-institutional cohort of 156 prostate cancer samples. Derived commercial biomarker scores for 120 informative primary prostate cancer samples from 44 cases were determined and compared.

RESULTS

Derived expression scores were positively correlated with tumor grade (rS = 0.53-0.73; all P < 0.001), both within the same case and across the entire cohort. In cases of extreme grade-discordant multifocality (co-occurrence of grade group 1 [GG1] and ≥GG4 foci], gene expression scores were significantly lower in low- (GG1) versus high-grade (≥GG4) foci (all P < 0.001). No significant differences in expression scores, however, were observed between GG1 foci from prostates with and without coexisting higher grade cancer (all P > 0.05).

CONCLUSIONS

Multifocal, low-grade and high-grade prostate cancer foci exhibit distinct prognostic expression signatures. These findings demonstrate that prognostic RNA expression assays performed on low-grade prostate cancer biopsy tissue may not provide meaningful information on the presence of coexisting unsampled aggressive disease.

FUNDING

Prostate Cancer Foundation, National Institutes of Health (U01 CA214170, R01 CA183857, University of Michigan Prostate Specialized Program of Research Excellence [S.P.O.R.E.] P50 CA186786-05, Weill Cornell Medicine S.P.O.R.E. P50 CA211024-01A1), Men of Michigan Prostate Cancer Research Fund, University of Michigan Comprehensive Cancer Center core grant (2-P30-CA-046592-24), A. Alfred Taubman Biomedical Research Institute, and Department of Defense.