Minimum Residual Disease in Patients Post Radical Prostatectomy for Prostate Cancer: Theoretical Considerations, Clinical Implications and Treatment Outcome

Tumor removal limits prostate cancer cell dissemination in bone and osteoblasts induce cancer cell dormancy through focal adhesion kinase

BACKGROUND

Disseminated tumor cells (DTCs) can enter a dormant state and cause no symptoms in cancer patients. On the other hand, the dormant DTCs can reactivate and cause metastases progression and lethal relapses. In prostate cancer (PCa), relapse can happen after curative treatments such as primary tumor removal. The impact of surgical removal on PCa dissemination and dormancy remains elusive. Furthermore, as dormant DTCs are asymptomatic, dormancy-induction can be an operational cure for preventing metastases and relapse of PCa patients.

METHODS

We used a PCa subcutaneous xenograft model and species-specific PCR to survey the DTCs in various organs at different time points of tumor growth and in response to tumor removal. We developed in vitro 2D and 3D co-culture models to recapitulate the dormant DTCs in the bone microenvironment. Proliferation assays, fluorescent cell cycle reporter, qRT-PCR, and Western Blot were used to characterize the dormancy phenotype. We performed RNA sequencing to determine the dormancy signature of PCa. A drug repurposing algorithm was applied to predict dormancy-inducing drugs and a top candidate was validated for the efficacy and the mechanism of dormancy induction.

RESULTS

We found DTCs in almost all mouse organs examined, including bones, at week 2 post-tumor cell injections. Surgical removal of the primary tumor reduced the overall DTC abundance, but the DTCs were enriched only in the bones. We found that osteoblasts, but not other cells of the bones, induced PCa cell dormancy. RNA-Seq revealed the suppression of mitochondrial-related biological processes in osteoblast-induced dormant PCa cells. Importantly, the mitochondrial-related biological processes were found up-regulated in both circulating tumor cells and bone metastases from PCa patients' data. We predicted and validated the dormancy-mimicking effect of PF-562,271 (PF-271), an inhibitor of focal adhesion kinase (FAK) in vitro. Decreased FAK phosphorylation and increased nuclear translocation were found in both co-cultured and PF-271-treated C4-2B cells, suggesting that FAK plays a key role in osteoblast-induced PCa dormancy.

CONCLUSIONS

Our study provides the first insights into how primary tumor removal enriches PCa cell dissemination in the bones, defines a unique osteoblast-induced PCa dormancy signature, and identifies FAK as a PCa cell dormancy gatekeeper.

A Systematic Review of Circulating Tumor Cells Clinical Application in Prostate Cancer Diagnosis

Simple Summary

Cell-dependent and cell-independent information drawn from the blood stream were merged into the attractive term “liquid biopsy” and tentatively applied to most segments of cancer management: detection, risk-stratification, personalization of care and follow-up. However, the robust science behind liquid biopsies has not been widely used, thereby remaining a latent and possibly undervalued instrument. Here, we conducted a systematic review of CTCs in prostate cancer management to summarize their use in clinical practice.

Abstract

The purpose of the review is to summarize the recent data on circulating tumor cells (CTC) use in clinical practice. We performed a systematic literature search using two databases (Medline and Scopus) over the past five years and the following terms: (CTC OR “circulating tumor cells” OR “liquid biopsy”) AND prostate. The primary outcome was CTC predictive value for prostate cancer (PC) progression and survival. The secondary outcomes were the CTC predictive value for therapy response and the results of CTC detection depending on the assessment method. In metastatic PC, the CTC count showed itself to be a prognostic marker in terms of clinically important features, namely survival rates and response to treatment. CTC concentration was significantly associated with the overall survival and progression-free survival rates. A strong association between the overall survival or progression-free survival rate and CTC concentration could be observed. Variant-7 androgen receptors-positive (AR-V7-positive) patients showed a poor response to androgen receptor signaling (ARS) inhibitors, but this did not compromise their response to taxanes. In localized PC, only positive Cluster of Differentiantion 82 protein (CD82+) correlated with a higher survival rate. CTC count and AR-V7 expression showed itself to be a valuable biomarker for survival in metastatic PC and response to ARS-inhibitors. CTC diagnostic performance for localized PC or for screening and early detection is not high enough to show additional value over the other biomarkers.

The CAPRA-S score versus subtypes of minimal residual disease to predict biochemical failure after radical prostatectomy

Objective

The objective of this study was to compare the CAPRA-S score (based on clinicopathological findings) and the subtypes of minimal residual disease (MRD) (based on the biological properties of cancer cells) to predict biochemical failure (BF) after prostatectomy radical.

Patients and methods

This was a prospective single-centre study of men who underwent radical prostatectomy. One month after surgery, the blood and bone marrow were taken for circulating prostate cell (CPC) and micrometastasis detection, identified using anti-PSA immunocytochemistry and defined as positive or negative. Patients were classified as Group A: CPC and micrometastasis negative, Group B: micrometastasis positive and CPC negative and Group C: CPC positive. CAPRA-S scores were classified as low, intermediate and high risk. Kaplan–Meier curves for biochemical failure-free survival (BFFS) and restricted mean survival time (RMST) to biochemical failure were determined and compared for up to 10 years.

Results

347 men participated with a median follow-up of 7 years, BFFS decreased proportionally with increasing CAPRA-S score and HR 1.13 and 1.65 for intermediate and high risk, respectively. After 10 years, the BFFS and RMST were 68%, 47% and 16% and 9, 7 and 6 years, respectively. The BFFS curves for MRD were not proportional; Group A and B BFFSs were similar up to 5 years, and then, there was an increasing failure in Group B patients After 10 years, the BFFS and RMST were 95%, 57% and 27% and 10, 9 and 6 years respectively. The CAPRA-S score failed to distinguish between Groups A and B, and one-third of high-risk Group C had low-risk CAPRA-S scores. MRD hazard ratios were Group B 1.76 and Group C 4.03.

Conclusions

The MRD prognostic classification was superior to the CAPRA-S score in predicting BFFS and differentiated between early and late BF. The results need to be confirmed in larger studies.

The Epstein criteria predict for organ-confined prostate cancer but not for minimal residual disease and outcome after radical prostatectomy

OBJECTIVE

The Epstein criteria (EC) used to select men for active surveillance do not predict biologically insignificant diseases. Minimal residual disease (MRD) is an undetected microscopic disease that remains after radical prostectomy (RP) and is a biological classification associated with the risk of treatment failure. Subtypes of MRD, the 10-year biochemical failure free survival (BFFS), and restricted mean biochemical failure free survival time (RMST) were determined and compared in EC patients treated with RP.

MATERIAL AND METHODS

Consecutive patients with a Gleason 6 biopsy treated at a single institution were divided into those who did or did not fulfill the EC and underwent RP. One month after surgery, samples were taken for the detection of circulating prostate cells (CPCs) and bone marrow micrometastasis. MRD was defined as negative for both CPCs and micrometastasis; patients were positive for micrometastasis and CPCs separately. BFFS for up to 10 years and RMST were determined for each MRD subgroup for EC positive and negative patients.

RESULTS

EC positive men (137/426) were significantly older (p<0.05) and had negative MRD, pT2 (pathologically organ confined) disease (<0.02), and lower frequency of upgrading (p<0.02). Of the EC positive men, 71% were MRD negative, 13% were positive for micrometastasis, and 16% were positive for CPCs with respective 10-year BFFS of 99%, 89%, and 21% (<0.001) (hazard ratio: 1.00, 1.76, 4.03, respectively) with no signficant differences between the 10-year BFFS or RMST for MRD subgroups for EC positive and negative patients.

CONCLUSIONS

EC predict pT2, MRD negative disease; however, 29% are MRD positive with a high risk of treatment failure.

The expression of matrix-metalloproteinase-2 in bone marrow micro-metastasis is associated with the presence of circulating prostate cells and a worse prognosis in men treated with radical prostatectomy for prostate cancer

OBJECTIVE

The expression of matrix-metalloproteinase-2 (MMP-2) in the primary tumor is associated with a worse prognosis but little is known at this time regarding the expression in micro-metastasis, the association with circulating prostate cells (CPCs), and outcome.

MATERIAL AND METHODS

This was a prospective study of men undergoing radical prostatectomy. Bone marrow and blood samples were taken at one month after surgery. Micro-metastasis and CPCs were identified using immunocytochemistry with anti-prostate specific-antigen and MMP-2 expression determined with anti-MMP-2. Pathological stage, Gleason score, and time to biochemical failure were recorded; meanwhile, Kaplan-Meier biochemical failure-free survival and restricted mean biochemical failure-free survival times for 10 years were determined.

RESULTS

A total of 282 men participated, 54 (19%) of whom had micro-metastasis but not CPCs (group B) and 88 (31%) of whom had micro-metastasis and CPCs (group C). Men in group C had a higher frequency of MMP-2 expressing micro-metastasis at 63% versus 12% (p<0.001), and MMP-2 expression in bone marrow micro-metastasis was associated with a higher Gleason score (p<0.05) as well as a higher frequency of and shorter time to treatment failure. Also, a 10-year Kaplan-Meier biochemical failure-free survival rate of 0% versus 7.7% (MMP-2 positive versus negative) and a mean time to biochemical failure of 2.6 versus 4.0 years were recorded.

CONCLUSION

The expression of MMP-2 in bone marrow micro-metastasis is associated with a higher Gleason score, the presence of CPCs, and a higher frequency of and shorter time to failure and could be clinically useful for identifying men at high risk of treatment failure.

Detection and isolation of disseminated tumor cells in bone marrow of patients with clinically localized prostate cancer

BACKGROUND

Disseminated tumor cells (DTCs) have been reported in the bone marrow (BM) of patients with localized prostate cancer (PCa). However, the existence of these cells continues to be questioned, and few methods exist for viable DTC isolation. Therefore, we sought to develop novel approaches to identify and, if detected, analyze localized PCa patient DTCs.

METHODS

We used fluorescence-activated cell sorting (FACS) to isolate a putative DTC population, which was negative for CD45, CD235a, alkaline phosphatase, and CD34, and strongly expressed EPCAM. We examined tumor cell content by bulk cell RNA sequencing (RNA-Seq) and whole-exome sequencing after whole genome amplification. We also enriched for BM DTCs with α-EPCAM immunomagnetic beads and performed quantitative reverse trancriptase polymerase chain reaction (qRT-PCR) for PCa markers.

RESULTS

At a threshold of 4 cells per million BM cells, the putative DTC population was present in 10 of 58 patients (17%) with localized PCa, 4 of 8 patients with metastatic PCa of varying disease control, and 1 of 8 patients with no known cancer, and was positively correlated with patients' plasma PSA values. RNA-Seq analysis of the putative DTC population collected from samples above (3 patients) and below (5 patients) the threshold of 4 putative DTCs per million showed increased expression of PCa marker genes in 4 of 8 patients with localized PCa, but not the one normal donor who had the putative DTC population present. Whole-exome sequencing also showed the presence of single nucleotide polymorphisms and structural variants in the gene characteristics of PCa in 2 of 3 localized PCa patients. To examine the likely contaminating cell types, we used a myeloid colony formation assay, differential counts of cell smears, and analysis of the RNA-Seq data using the CIBERSORT algorithm, which most strongly suggested the presence of B-cell lineages as a contaminant. Finally, we used EPCAM enrichment and qRT-PCR for PCa markers to estimate DTC prevalence and found evidence of DTCs in 21 of 44 samples (47%).

CONCLUSION

These data support the presence of DTCs in the BM of a subset of patients with localized PCa and describe a novel FACS method for isolation and analysis of viable DTCs.

Effect of FOLFOX on minimal residual disease in Stage III colon cancer and risk of relapse

Introduction

25% of Stage III colon cancer patients relapse within 5 years due to minimal residual disease (MRD) not eliminated by surgery and chemotherapy. We hypothesise that sub-types of MRD, defined by circulating tumour cells (CTCs) and bone marrow micro-metastasis (mM) have different types and kinetics of relapse.

Patients and Methods

One month of curative surgery and 1 month after completing six cycles of FOLFOX chemotherapy blood and bone marrow samples were taken to detect CTCs and mM using immunocytochemistry with anti-carcino-embryonic antigen (CEA). Follow up was up to 5 years or disease progression defined as new images on CT scanning. Survival curves using Kaplan–Meier (KM) and Restricted Mean Survival Time (RMST) were calculated for three prognostic groups: CTC and mM negative, CTC negative mM positive, and CTC positive.

Results

76 patients (39 men) participated, mean age 67 years, median follow-up 3.6 years. The response to chemotherapy was heterogeneous and MRD pre-treatment did not predict response to therapy. Of 21 patients MRD (−), 20 remained MRD negative and one patient became mM (+); of 21 patients mM (+), 10 became MRD (−), 8 remained the same and 3 became CTC (+); of the 34 CTC positive, 8 became MRD (−), 8 with only mM, and 18 remained positive.

After chemotherapy, 38 patients were negative for CTC and mM, 17 were positive for only mM, and 21 for CTCs. For the whole cohort, the 5 year KM was 58%, the median survival was not reached. For the three prognostic groups, the KM 5-year survivals were 87%, 58%, and 4%, respectively, the median survival for patients MRD negative and mM only was not reached. RMST for the whole cohort was 3.6 years, for the three prognostic groups the RMST was 4.6 years, 4.0 years, and 1.5 years, respectively. Serum CEA was significantly higher pre-surgery in the CTC positive group. There were no significant differences with respect to age or sex between the three groups.

Conclusions

MRD subtypes pre-chemotherapy did not predict treatment response. Post-chemotherapy MRD subtypes were associated with the pattern of failure and time to failure. MRD negative patients had an excellent prognosis with 87% disease-free survival at 5 years. Those with only mM had a similar outcome up to 2 years and then were at increasing risk of late failure. Patients who were CTC positive had a high risk of early failure. MRD subclassification may be useful to define the risk of relapse in Stage III colon cancer patients and warrants further studies with a larger number of patients.

Subtypes of minimal residual disease, association with Gleason score, risk and time to biochemical failure in pT2 prostate cancer treated with radical prostatectomy

Introduction

The Gleason score is a strong prognostic factor for treatment failure in pathologically organ-confined prostate cancer (pT2) treated by radical prostatectomy (RP). However, within each Gleason score, there is clinical heterogeneity with respect to treatment outcome, even in patients with the same pathological stage and prostate-specific antigen (PSA) at diagnosis. This may be due to minimal residual disease (MRD) remaining after surgery. We hypothesise that the sub-type of MRD determines the risk of and timing of treatment failure, is a biological classification, and may explain in part clinical heterogeneity. We present a study of pT2 patients treated with RP, the subtypes of MRD for each Gleason score and clinical outcomes.

Patients and methods

Patients with Gleason ≤6 (G6) or Gleason 7 (G7) pT2 cancer participated in the study. One month after surgery, blood was taken for circulating prostate cell (CPCs); mononuclear cells were obtained by differential gel centrifugation and identified using immunocytochemistry with anti-PSA. The detection of one CPC/sample was defined as a positive test. Touch-preparations from bone-marrow biopsies were used to detect micro-metastasis using immunocytochemistry with anti-PSA. Biochemical failure was defined as a PSA >0.2 ng/mL. Patients were classified as: Group A MRD negative (CPC and micro-metastasis negative), Group B (only micro-metastasis positive) and Group C (CPC positive). Biochemical failure-free survival (BFFS) using Kaplan–Meier and time to failure using Restricted Mean Survival Time (RMST) after 10 years of follow-up were calculated for each group based on the Gleason score.

Results

Of a cohort of 253 men, four were excluded for having Gleason 8 or 9 prostate cancer, leaving a study group of 249 men of whom 52 had G7 prostate cancer. G7 patients had a higher frequency of MRD (69% versus 36%) and worse prognosis. G6 and G7 patients negative for MRD had similar BBFS rates, 98% at 10 years, time to failure 9.9 years. Group C, G6 patients had a higher BFFS and longer time to failure compared to G7 patients (19% versus 5% and 7 versus 3 years). Group B showed similar results up to 5 years, thereafter G6 had a lower BFFS 63% versus 90%.

Conclusions

G7 and G6 pT2 patients have different patterns of MRD and relapse. Risk stratification using MRD sub-types may help to define the need for adjuvant therapy. This needs confirmation with large randomised long-term trials.

Parallels between hematopoietic stem cell and prostate cancer disseminated tumor cell regulation

The bone marrow is the primary site of hematopoiesis and the home for hematopoietic stem cells (HSCs) in adult mammals. Prostate cancer commonly metastasizes to the bone and forms bone metastases in almost all patients who die of the disease. Prostate cancer bone metastases are thought to develop after rare bone marrow disseminated tumor cells (DTCs) escape a dormant state and reactivate. Prostate cancer DTCs and normal HSCs have been shown to compete for residence in the bone marrow and share many of same regulatory mechanisms for survival, proliferation and homing. In this review, we highlight these parallels in order to help our readers use the literature in HSC and DTC biology to inform their research and generate hypotheses in both fields.

Minimal residual disease in prostate cancer patients after primary treatment: theoretical considerations, evidence and possible use in clinical management

Minimal residual disease is that not detected by conventional imaging studies and clinically the patient remains disease free. However, with time these dormant cells will awaken and disease progression occurs, resulting in clinically and radiological detectable metastatic disease. This review addresses the concept of tumor cell dissemination from the primary tumor, the micrometastatic niche and tumor cell survival and finally the clinical utility of detecting and characterizing these tumor cells in order to guide management decisions in treating patients with prostate cancer.

The presence of secondary circulating prostate tumour cells determines the risk of biochemical relapse for patients with low- and intermediate-risk prostate cancer who are treated only with external radiotherapy

Introduction

The classification of patients with prostate cancer is used to determine treatments based on risk factors. The presence of secondary circulating prostate tumour cells (CPCs) detected in peripheral blood after a curative treatment has been associated with a worse prognosis. We present a prospective study of CPC detection post radiotherapy and the oncological results.

Patients and methods

All of the patients classified as low and intermediate risk that were treated with radiotherapy were included. Three months after finishing treatment, an 8-ml blood sample was taken to detect CPCs. Mononuclear cells were obtained using gel centrifugation, and CPCs were identified using immunocytochemistry with anti-prostate-specific antigen. Patients were classified as low-risk CPC positive or negative and intermediate-risk CPC positive or negative. The biochemical relapse-free survival analysis was determined based on a follow-up of up to 15 years using the Kaplan–Meier and Cox regression models. Biochemical failure was defined according to the Pheonix II criteria.

Results

Of 241 patients, 181 (75.1%) were classified as low risk and 60 (24.9%) as intermediate risk. Biochemical failure was observed in 27.1% (49/181) of the low-risk prostate cancer participants and in 53.3% (32/60) of intermediate-risk participants after 15 years of follow-up. 20.4% (37/181) of the low-risk cancer participants had detectable CPCs in comparison with 43.3% (26/60) of the intermediate-risk cancer participants (p < 0.001 overall risk 2.98, confidence interval (CI) 95% 1.59–5.56; relative risk 2.12, CI 95% 1.41–3.19). Positive CPC patients had a worse prognosis, and a shorter time period until biochemical relapse, regardless of risk group. The biochemical relapse-free survival curves show that intermediate-risk participants who were CPC negative had a higher survival rate and slower disease progression than those participants who were low risk but CPC positive.

Conclusions

CPC detection is a risk factor for biochemical relapse and could be useful in identifying patients that will need additional treatment.