False positive PSMA PET for tumor remnants in the irradiated prostate and other interpretation pitfalls in a prospective multi-center trial

Purpose

Readers need to be informed about potential pitfalls of [⁶⁸Ga]Ga-PSMA-11 PET interpretation.

Methods

Here we report [⁶⁸Ga]Ga-PSMA-11 PET findings discordant with the histopathology/composite reference standard in a recently published prospective trial on 635 patients with biochemically recurrent prostate cancer.

Results

Consensus reads were false positive in 20 regions of 17/217 (8%) patients with lesion validation. Majority of the false positive interpretations (13 of 20, 65%) occurred in the context of suspected prostate (bed) relapse (T) after radiotherapy (n = 11); other false positive findings were noted for prostate bed post prostatectomy (T, n = 2), pelvic nodes (N, n = 2), or extra pelvic lesions (M, n = 5). Major sources of false positive findings were PSMA-expressing residual adenocarcinoma with marked post-radiotherapy treatment effect. False negative interpretation occurred in 8 regions of 6/79 (8%) patients with histopathology validation, including prostate (bed) (n = 5), pelvic nodes (n = 1), and extra pelvic lesions (n = 2). Lesions were missed mostly due to small metastases or adjacent bladder/urine uptake.

Conclusion

[⁶⁸Ga]Ga-PSMA-11 PET at biochemical recurrence resulted in less than 10% false positive interpretations. Post-radiotherapy prostate uptake was a major source of [⁶⁸Ga]Ga-PSMA-11 PET false positivity. In few cases, PET correctly detects residual PSMA expression post-radiotherapy, originating however from treated, benign tissue or potentially indolent tumor remnants.

Trial registration number

ClinicalTrials.gov Identifiers: NCT02940262 and NCT03353740.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04945-1) contains supplementary material, which is available to authorized users.

Mutational Landscape of Aggressive Prostate Tumors in African American Men

Prostate cancer is the most frequently diagnosed and second most fatal nonskin cancer among men in the United States. African American men are two times more likely to develop and die of prostate cancer compared with men of other ancestries. Previous whole genome or exome tumor-sequencing studies of prostate cancer have primarily focused on men of European ancestry. In this study, we sequenced and characterized somatic mutations in aggressive (Gleason ≥7, stage ≥T2b) prostate tumors from 24 African American patients. We describe the locations and prevalence of small somatic mutations (up to 50 bases in length), copy number aberrations, and structural rearrangements in the tumor genomes compared with patient-matched normal genomes. We observed several mutation patterns consistent with previous studies, such as large copy number aberrations in chromosome 8 and complex rearrangement chains. However, TMPRSS2-ERG gene fusions and PTEN losses occurred in only 21% and 8% of the African American patients, respectively, far less common than in patients of European ancestry. We also identified mutations that appeared specific to or more common in African American patients, including a novel CDC27-OAT gene fusion occurring in 17% of patients. The genomic aberrations reported in this study warrant further investigation of their biologic significant role in the incidence and clinical outcomes of prostate cancer in African Americans. Cancer Res; 76(7); 1860-8. ©2016 AACR.

miR-19, miR-345, miR-519c-5p serum levels predict adverse pathology in prostate cancer patients eligible for active surveillance

Serum microRNAs hold great promise as easily accessible and measurable biomarkers of disease. In prostate cancer, serum miRNA signatures have been associated with the presence of disease as well as correlated with previously validated risk models. However, it is unclear whether miRNAs can provide independent prognostic information beyond current risk models. Here, we focus on a group of low-risk prostate cancer patients who were eligible for active surveillance, but chose surgery. A major criteria for the low risk category is a Gleason score of 6 or lower based on pre-surgical biopsy. However, a third of these patients are upgraded to Gleason 7 on post surgical pathological analysis. Both in a discovery and a validation cohort, we find that pre-surgical serum levels of miR-19, miR-345 and miR-519c-5p can help identify these patients independent of their pre-surgical age, PSA, stage, and percent biopsy involvement. A combination of the three miRNAs increased the area under a receiver operator characteristics curve from 0.77 to 0.94 (p<0.01). Also, when combined with the CAPRA risk model the miRNA signature significantly enhanced prediction of patients with Gleason 7 disease. In-situ hybridizations of matching tumors showed miR-19 upregulation in transformed versus normal-appearing tumor epithelial, but independent of tumor grade suggesting an alternative source for the increase in serum miR-19a/b levels or the release of pre-existing intracellular miR-19a/b upon progression. Together, these data show that serum miRNAs can predict relatively small steps in tumor progression improving the capacity to predict disease risk and, therefore, potentially drive clinical decisions in prostate cancer patients. It will be important to validate these findings in a larger multi-institutional study as well as with independent methodologies.

Successful whole-exome sequencing from a prostate cancer bone metastasis biopsy

BACKGROUND

Comprehensive molecular characterization of cancer that has metastasized to bone has proved challenging, which may limit the diagnostic and potential therapeutic opportunities for patients with bone-only metastatic disease.

METHODS

We describe successful tissue acquisition, DNA extraction, and whole-exome sequencing from a bone metastasis of a patient with metastatic, castration-resistant prostate cancer (PCa).

RESULTS

The resulting high-quality tumor sequencing identified plausibly actionable somatic genomic alterations that dysregulate the phosphoinostide 3-kinase pathway, as well as a theoretically actionable germline variant in the BRCA2 gene.

CONCLUSIONS

We demonstrate the feasibility of diagnostic bone metastases profiling and analysis that will be required for the widespread application of prospective 'precision medicine' to men with advanced PCa.

Incomplete inhibition of phosphorylation of 4E-BP1 as a mechanism of primary resistance to ATP-competitive mTOR inhibitors

The mammalian target of rapamycin (mTOR) regulates cell growth by integrating nutrient and growth factor signaling and is strongly implicated in cancer. But mTOR is not an oncogene, and which tumors will be resistant or sensitive to new ATP-competitive mTOR inhibitors now in clinical trials remains unknown. We screened a panel of over 600 human cancer cell lines to identify markers of resistance and sensitivity to the mTOR inhibitor PP242. RAS and PIK3CA mutations were the most significant genetic markers for resistance and sensitivity to PP242, respectively; colon origin was the most significant marker for resistance based on tissue type. Among colon cancer cell lines, those with KRAS mutations were most resistant to PP242, while those without KRAS mutations most sensitive. Surprisingly, cell lines with co-mutation of PIK3CA and KRAS had intermediate sensitivity. Immunoblot analysis of the signaling targets downstream of mTOR revealed that the degree of cellular growth inhibition induced by PP242 was correlated with inhibition of phosphorylation of the translational repressor 4E-BP1, but not ribosomal protein S6. In a tumor growth inhibition trial of PP242 in patient-derived colon cancer xenografts, resistance to PP242 induced inhibition of 4E-BP1 phosphorylation and xenograft growth was again observed in KRAS mutant tumors without PIK3CA co-mutation, compared to KRAS WT controls. We show that, in the absence of PIK3CA co-mutation, KRAS mutations are associated with resistance to PP242 and that this is specifically linked to changes in the level of phosphorylation of 4E-BP1.

Diversity of antigen-specific responses induced in vivo with CTLA-4 blockade in prostate cancer patients

CTLA-4 is a surface receptor on activated T cells that delivers an inhibitory signal, serving as an immune checkpoint. Treatment with anti-CTLA-4 Abs can induce clinical responses to different malignancies, but the nature of the induced Ag-specific recognition is largely unknown. Using microarrays spotted with >8000 human proteins, we assessed the diversity of Ab responses modulated by treatment with CTLA-4 blockade and GM-CSF. We find that advanced prostate cancer patients who clinically respond to treatment also develop enhanced Ab responses to a higher number of Ags than nonresponders. These induced Ab responses targeted Ags to which preexisting Abs are more likely to be present in the clinical responders compared with nonresponders. The majority of Ab responses are patient-specific, but immune responses against Ags shared among clinical responders are also detected. One of these shared Ags is PAK6, which is expressed in prostate cancer and to which CD4(+) T cell responses were also induced. Moreover, immunization with PAK6 can be both immunogenic and protective in mouse tumor models. These results demonstrate that immune checkpoint blockade modulates Ag-specific responses to both individualized and shared Ags, some of which can mediate anti-tumor responses.

An aberrant prostate antigen-specific immune response causes prostatitis in mice and is associated with chronic prostatitis in humans

Chronic prostatitis is a common disease of unclear etiology and has no specific treatment. Mice deficient in the expression of the autoimmune regulator (Aire) gene, which are defective in thymic expression of self antigens and central tolerance, develop spontaneous prostatitis. In this study, we found that Aire-deficient mice developed spontaneous B and T cell immune responses to a prostate autoantigen, seminal vesicle secretory protein 2 (SVS2), which we believe to be novel. We show that thymic expression of this self antigen was Aire dependent. Moreover, prostatitis was induced in WT mice through immunization with SVS2, demonstrating that immunity to SVS2 was sufficient to induce prostatitis. The clinical relevance of this antigen was highlighted by our observation that patients with chronic prostatitis possessed specific autoantibodies against the human SVS2-like seminal vesicle protein semenogelin. These results provide direct evidence that spontaneous chronic prostatitis is an autoimmune disease and is regulated by both central and peripheral tolerance. Moreover, SVS2 and semenogelin are among the relevant autoantigens in mice and humans, respectively.

The independent impact of extended pattern biopsy on prostate cancer stage migration

PURPOSE

There are many factors impacting stage migration for prostate cancer. The number of prostate core biopsies is known to increase detection of prostate cancers. It is still unknown whether the number of biopsies is an independent predictor of tumor size. This is important as a number of studies show that tumor volume is an independent predictor of cancer progression.

MATERIALS AND METHODS

Using the University of California, San Francisco Urologic Oncology database, a retrospective review of 378 patients undergoing radical prostatectomy by a single surgeon during 2000 to 2003 was performed. Patient and tumor specific variables including age, prostate specific antigen (PSA), number of biopsies, biopsy Gleason grade, tumor volume in the surgical specimen and surgical specimen tumor grade were studied. Univariate and multivariate statistical methods including multiple and logistic regression were used to characterize patients by the number of biopsy cores. Tests of significance to identify predictors of tumor size were based on the partial F statistic and the likelihood ratio test.

RESULTS

A total of 317 eligible patients were studied, of whom 119 had 6 biopsies and 198 had more than 6 biopsies. The 2 groups of patients were evenly matched in terms of age, PSA and Gleason sum, with no statistically significant differences observed. On univariate analysis, mean tumor volume was larger for patients receiving 6 core biopsies vs greater than 6 core biopsies (3.85 vs 2.04 cc, p = 0.0009). Additionally, statistically significant differences were observed when comparing median tumor volumes, as well as excluding extremely large volume tumors. On multivariate analysis the number of biopsies performed (6 vs more than 6), was an independent predictor of tumor size (p = 0.006), controlling for primary Gleason score, Gleason sum, PSA as a continuous or categorical variable, year of biopsy and year of surgery.

CONCLUSIONS

The use of extended pattern prostate biopsy templates results in the detection of smaller volume prostate cancers, independent of PSA and Gleason grade. These biopsy templates have contributed to the downward stage migration of prostate cancer detection and may possibly contribute to the risk of over detection.