According to the 2015 Annual Report of the National Central Cancer Registry (China), the overall incidence of prostate cancer was 7.1/105 individuals in 2011. Accordingly, prostate cancer was the ninth most prevalent cancer overall, and seventh most prevalent among men [23]. However, the majority of patients with prostate cancer were diagnosed at an advanced disease stage. Early diagnosis is a key driver of improved survival among men with prostate cancer in China. Organ-confined prostate cancer at the time of diagnosis is associated with a good prognosis and a favourable response to curative therapy [24]. Conversely, metastatic prostate cancer is associated with a poor prognosis, and skeletal metastasis is associated with a 5-year survival rate of <30% [25].
In the present study, 13 patients presented with indications of prostate cancer, including an elevated PSA level and/or abnormal digital rectal examination and/or imaging findings. One patient had been treated previously for prostate cancer. According to the 18F-FDG PET/CT findings, 6 patients (66.7%) with prostate cancer had skeletal metastases, and 1 patient (11.1%) presented with a tumour that was no longer organ-confined and had invaded the bladder. The incidence rate of multiple primary tumours among patients with prostate cancer was 28.6% (4/14).
Improvements in cancer care have been linked closely to advances in imaging technologies, as these improvements enable a more accurate diagnosis, staging, and surveillance of disease. PET/CT recently emerged as a promising diagnostic imaging platform for both primary and recurrent prostate cancers [26]. In addition to 18F-FDG, routine clinical imaging procedures use various radiolabelled tracers [e.g., 18F-choline,18F-NaF, 68Ga-prostate-specific membrane antigen (PSMA), 68Ga-DOTATATE, 18F-FACBC] with demonstrated efficacy for cancer diagnosis in various clinical settings [26-27]. Newly developed tracers exhibit increased accuracy for the detection of small, incipient metastatic foci [28-29]. Improvements in MRI techniques, and particularly in functional imaging, have enabled radiologists to play an important role in the risk stratification and management of patients [30-32].
18F-FDG PET/CT is primarily useful in the diagnosis and staging of prostate cancer because it combines the metabolic information of PET with the anatomic information of CT. Moreover, whole-body scanning facilitates the detection of primary tumours in multiple organs. Additionally, 18F-FDG PET/CT can accurately diagnose cancer recurrence. In this study, prostate cancer was confirmed via histopathological examinations in 9 of 14 patients, whereas the remaining 5 patients had benign lesions (including 2 misdiagnoses of prostate cancer). The diagnostic accuracy of 18F-FDG PET/CT for prostate cancer was 81.8% (9/11). Of the 14 patients, we detected multiple primary tumours that were confirmed pathologically as prostate cancer in 4 patients (28.6%). One of the 9 patients exhibited a tumour recurrence and metastatic bone lesion on 18F-FDG PET/CT, which was eventually confirmed as prostate cancer.
Despite the enthusiasm surrounding the use of PET and MRI for diagnosing prostate cancer, prostate biopsy remains the gold-standard diagnostic option. Prostate biopsies have been used to diagnose prostate cancer since the beginning of the last century [5-6]. Ideally, prostate biopsy should be minimally invasive with few side effects, and should identify a large proportion of men who would benefit from treatment while minimising the identification of men with clinically insignificant cancer to prevent over-treatment. Although the optimal method of prostate biopsy remains controversial, TRUS-guided biopsy is the most widely accepted method for the diagnosis of prostate cancer. Greyscale TRUS has a low sensitivity and specificity for prostate cancer detection, and some studies reported low detection rates for saturation prostate biopsy via the trans-rectal or trans-perineal route (21.7–45% [33-36] and 22.7–42.2%, respectively [37-39]). Despite the advantages of TRUS-guided prostate biopsy, its invasive nature and rectal approach could potentially cause complications. Infectious complications ranging from asymptomatic bacteriuria to septic shock may occur during TRUS-guided prostate biopsy via the manipulation of infected prostate tissue, which also increases the risk of introducing the rectal flora into the prostate tissue, urine, and blood.
Here, we introduce a novel approach to prostate biopsy, namely 18F-FDG PET/CT-guided percutaneous trans-pararectal space prostate biopsy. PET/CT is a widely accepted modality for detecting prostatic lesions and identifying cancer recurrence and metastasis, particularly when conventional imaging findings are equivocal or conflicting. PET/CT also increases the choice of biopsy location, which can increase the associated accuracy and safety.
Besides the primary lesion, PET/CT also enables the biopsy of other metabolically active lesions, such as metastatic bone lesions that cannot be detected using conventional imaging methods. In such cases, PET/CT-guided biopsy allows the sampling of multiple hypermetabolic lesions, thereby reducing false-negative or false-positive biopsy rates. In our study, PET/CT-guided biopsies were performed in 14 patients with indications of prostate cancer based on PET/CT images. The 4th patient in our study underwent prostate, lung, and iliac bone biopsy under PET/CT guidance, despite the lack of apparent bone morphological changes on a CT scan. The histopathological analysis revealed that both the prostatic and pulmonary lesions had originated from the primary prostate tumour, whereas the bone lesions had metastasised from the lung lesion rather than the prostate tumour.
Before performing PET/CT-guided percutaneous 18F-FDG-avid target biopsy, we selected the optimal puncture site based on the target location to ensure a favourable biopsy success rate and the optimal needle path to minimise trauma. When selecting the target location, the site with the highest metabolic 18F-FDG accumulation among all focal hypermetabolic prostate lesions was selected first, as such lesions would more likely represent the true cancer grade and would thus affect the clinical classification, staging, and prognosis. Other visible but controversial lesions were targeted thereafter.
The optimal needle path is extremely important when aiming to avoid puncturing the nearby blood vessels, spinal nerve trunk, and other vital organs. In our study, we chose the anatomically safer trans-pararectal space, rather than the trans-rectal or trans-perineal approach. This option can avoid the damage to the rectum or perineum associated with a conventional biopsy path, and may minimise the occurrence of complications. Altogether, we considered these factors to ensure a safe, feasible, and effective prostate biopsy procedure. 18F-FDG PET/CT-guided percutaneous trans-pararectal space prostate biopsy is the third prostate biopsy technique worldwide that can accommodate all these factors simultaneously. This novel method can reduce the false-negative or false-positive rate and is a relatively safer and more effective way to obtain a pathological diagnosis.
In our study, a correct biopsy-assisted diagnosis was made on all cases. The diagnostic success of 18F-FDG PET/CT-guided percutaneous trans-pararectal space prostate biopsy was 100.0% (14/14). Simultaneous PET/CT-guided targeted biopsies of the prostate and other organs were performed in 57.1% (8/14) of the patients. Finally, histopathological examination confirmed the presence of primary prostate lesions in 4 patients. In summary, 18F-FDG PET/CT-guided percutaneous trans-pararectal space prostate biopsy mitigates the issue of trans-visceral puncture trauma by accurate biopsy, and enables a pathological diagnosis from a smaller tissue volume. Moreover, the ability to biopsy other organs simultaneously provides additional diagnostic possibilities, thus avoiding an unnecessary diagnosis or over-treatment.
Our study had several limitations. First, the small sample size might have limited the statistical significance of the results. Second, 18F-FDG PET/CT is associated with some disadvantages. For example, small tumours might remain undetected because of partial-volume effects, which would cause falsely low measurements of the true 18F-FDG activity level. Moreover, 18F-FDG frequently accumulates in areas of inflammation. However, physiological variants and benign pathological causes of 18F-FDG uptake can be recognised specifically and categorised properly using other approaches. Accordingly, we will evaluate the efficacy of 68Ga-PSMA PET/CT-guided prostate biopsy in a future study.