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Current imaging trends for prostate cancer diagnosis

Chris_McNamara
Community Manager
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Current imaging trends for prostate cancer diagnosis

By Kalli Spencer

Imaging for newly diagnosed prostate cancer patients is evolving rapidly, with the introduction of multiparametric magnetic resonance imaging (mpMRI) and positron emission tomography (PET). Traditionally, staging for prostate cancer is recommended in higher risk groups, and is usually performed with computerised tomography (CT) and whole‐body technetium bone scans. Such imaging modalities are, however, limited in their accuracy, especially in patients with a single metastatic site and at low prostate specific antigen (PSA) levels.

New imaging technology, using prostate specific membrane antigen (PSMA) PET combined with computerised tomography (PET/CT), has proven highly useful for staging prostate cancer in both the newly diagnosed and recurrent setting (disease that has returned after primary treatment). Benefits include greater utility in making treatment decisions and lower radiation doses.

In newly diagnosed prostate cancer cases, accurately excluding metastatic disease allows classification of patients with disease only localised to the prostate to either undergo a radical prostatectomy (RP) or radiotherapy (RT). If metastatic disease is not identified at the time of initial diagnosis there may be an elevated risk of disease progression after treatment for what was presumed localised disease. The potential of diagnosing metastatic disease at an earlier stage is increasingly being recognised, as low‐volume metastatic cancer may benefit from treatment with combined systemic and radiation therapies.

Despite its proven success and widespread use in Europe and Australia, the uptake of PSMA PET has been limited in several other countries. Numerous groups have suggested that PSMA PET should only occur in a clinical trial setting. The regulatory environment in Australia allows relatively unregulated use of imaging agents such as 68Ga‐PSMA, thus making it widely available in Australia for paying patients. The precise practice patterns of PSMA PET in primary staging for prostate cancer in a population have not been reported in previous literature. A study by Papa N et al1 set out to demonstrate the patterns of primary staging of prostate cancer in Victoria, Australia using prostate cancer registry data.

The Prostate Cancer Outcomes Registry‐Victoria (PCOR‐Vic) is a database of men with prostate cancer whose cases were managed across Victoria. In 2017–2018, the estimated population coverage of PCOR‐Vic was in excess of 75%.

Men included in the analysis had been diagnosed with prostate cancer by prostate biopsy or transurethral resection of the prostate (TURP) from October 2016 (the earliest time that staging imaging was consistently collected). Conventional imaging (CImg) was defined as receiving staging CT and/or bone scan. If the imaging was performed within 180 days before or after the diagnostic procedure, a staging modality type ‘PET with or without CImg’ or ‘CImg without PET’ was assigned. The category of ‘neither recorded’ was assigned if no staging PET, CT or bone scan was recorded in the registry at any time.

To align prostate grading classifications with other cancers where low risk is Group 1 and high risk is Group 5, the International Society of Urological Pathology (ISUP) made the following change to the older Gleeson Histological grading system:

Gleeson score: 3+3=6    is ISUP Grade Group 1

Gleeson score: 3+4=7    is ISUP Grade Group 2

Gleeson score: 4+3= 7   is ISUP Grade Group 3

Gleeson score: 4+4=8    is ISUP Grade Group 4

Gleeson score: 5+5=10  is ISUP Grade Group 5

 

For conventional prostate cancer risk stratification, the following definitions are used:

Low risk: Grade Group 1 and PSA<10

Intermediate risk (Further classified into favourable and unfavourable)

Favourable intermediate risk - Grade Group 2 or less PSA >10 and <20, <50% of biopsy cores positive

Unfavourable intermediate risk - Grade Group 3 and PSA >10 and <20, >50% of biopsy cores positive

High risk: Grade Group 4 or 5 and PSA >20

 

In this study patients were risk stratified as follows:

  • ‘low risk’ (Histological [ISUP] Grade group 1/2 and PSA < 10 ng/mL)
  • ‘high risk’ (Histological [ISUP] Grade group 2 AND PSA ≥ 10 ng/mL OR Grade group 3+).

Treatments administered were classified as either systemic (chemotherapy, ADT) or interventional (radiotherapy, surgery).

In the period October 2016 to December 2018 inclusive, a total of 6139 patients in PCOR‐Vic were diagnosed with prostate cancer by biopsy or an incidental finding during a TURP for a benign enlargement of the prostate causing urination difficulty.

The results were as follows:

  • 14% had a staging PET/CT scan performed within 180 days of diagnosis
  • 40% had staging with conventional imaging but no PET scan within 180 days of diagnosis
  • 45% had no recorded PET, CT or bone scan at any time

The proportion of all patients receiving staging PET increased over the study period from 11% for men diagnosed in the initial three months, to 20% in the final three months. This was most pronounced for patients classified as ‘high risk’, with the increase being from 19% to 33%. Of the patients with any recorded imaging, the proportion that underwent PET increased from 19% to 36% and from 23% to 43% for high-risk men.

Using registry‐based data, the researchers highlighted the increasing use of PET imaging in primary staging of prostate cancer, particularly in high-risk disease. Associated with this increased use of PET, there has been an increase in the diagnosis of metastatic nodal disease. Furthermore, despite the recommendations of rationalising imaging in favourable intermediate risk disease, a substantial proportion of men still undergo staging prior to definitive therapy.

The findings of the study highlight ‘real‐world’ data regarding the use in practice of PET for the primary staging of prostate cancer in Australia, where PSMA PET/CT has been widely available for a number of years. Notwithstanding this evidence, limited data is available addressing the clinical uptake of PET/CT imaging for prostate cancer. Numerous groups have suggested that PSMA PET/CT should only occur in the clinical trial setting. The researchers’ findings based on registry data quantify the rapid increase of PET/CT in routine clinical practice for primary staging of prostate cancer in Victoria, particularly for patients residing in major urban areas. These results align with recent literature suggesting declining use of whole-body bone scans and increased uptake of PSMA PET/CT. The rise in utilisation of such imaging is likely due to increased awareness and confidence in this imaging type. This may be in part due to the early adoption and prolonged clinical experience of PSMA PET/CT within the country. Over time, accessibility has become more widespread, with some regional centres across the country having satisfactory PSMA availability. The familiarity and confidence in the data supporting its use and improved access to PSMA have largely driven its uptake.

This registry‐based study demonstrated higher rates of diagnosis of nodal disease in patients staged with PSMA PET imaging compared with conventional imaging. Unidentified nodal metastatic disease prior to definitive treatment may exacerbate the risk of cancer recurrence. These properties of PSMA PET/CT have clinically significant implications on the management strategies of these patients, as they may no longer be suitable for local therapy (RP or RT) and could benefit from systemic therapies such as androgen deprivation. Conversely, patients who might otherwise have benefitted from local therapy may be denied this opportunity as there is no data to show the oncological benefit, if any, of using PSMA PET/CT as a primary staging tool.

Despite recommendations by leading bodies, the researchers’ results indicate that a substantial proportion of men with intermediate risk prostate cancer are undergoing systemic imaging. Current European Association of Urology (EAU) guidelines recommend imaging studies for newly diagnosed ‘high risk’ prostate cancer. Similarly, the American Urological Association (AUA) recommends imaging for staging in patients with ‘unfavourable intermediate risk disease’. According to the researchers’ registry data, 32% of patients with ‘favourable intermediate risk disease’ are undergoing primary staging. Of these patients who did receive imaging for staging, only 0.7% had detected metastatic disease. This finding highlights the low yield of imaging in these patients. These observations support the EAU and AUA recommendations to primarily image patients with unfavourable intermediate risk or high‐risk prostate cancer.

In conclusion, the study provides a contemporary snapshot of the rapidly evolving landscape of primary staging for prostate cancer. The researchers’ registry data highlights the adoption of PSMA PET imaging, particularly in high-risk disease. They highlight the increased diagnosis of nodal disease – and thus the potential to optimize patient selection prior to definitive treatment. They also observed different treatment patterns for men with regional node or metastatic disease, depending on the staging image modalities used. A recommendation was made that future research could focus on a cost‐benefit analysis and the impact of novel imaging on survival.

Reference:

Papa N, Perera M, Murphy DG, Lawrentschuk N, Evans M, Millar JL, Bolton D. Patterns of primary staging for newly diagnosed prostate cancer in the era of prostate specific membrane antigen positron emission tomography: A populationbased analysis. Journal of Medical Imaging and Radiation Oncology. 05/03/2021. Online version ahead of print.

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About the Author

 

Kalli Spencer

MBBCh, FC Urol (SA), MMed (Urol), Dip.Couns (AIPC)

 

Kalli is an internationally renowned Urological Surgeon, specialising in oncology and robotic surgery. He trained and worked in South Africa, before relocating to Australia where he has worked at Macquarie University Hospital and Westmead Hospital. His passion for what he does extends beyond the operating room, through public health advocacy, education and community awareness of men’s health, cancer and sexuality.

 

Kalli has been involved with the Prostate Cancer Foundation of Australia for many years, advocating for improved cancer care and facilitating community prostate cancer support groups.

 

 

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