Role of transperineal template biopsy in prostate cancer

Abstract

Prostate cancer is the most common neoplasm diagnosed in men. Whilst treatment modalities have progressed, diagnostic investigations in terms of biopsy methods have been assessed but there is no consensus of when the different diagnostic methods in terms of transrectal ultrasound (TRUS) or transperineal template (TPT) should be utilised. TPT biopsy has a higher diagnostic yield than TRUS in those with a primary biopsy, in those with previous negative biopsies with TRUS as well as those undergoing saturation biopsies. Despite the increased likelihood of diagnosing cancer with TPT than TRUS this maybe secondary to the increased number of biopsies being utilised. However there is no consensus regarding the ideal number of biopsies that should be utilised with TPT. Furthermore it is felt that the increased number of biopsies utilised with TPT is associated the higher complication rates with TPT. The role of TPT biopsy is recognised in those with previous negative biopsies with transrectal ultrasound but further work is required regarding the ideal number of biopsies. Furthermore, it is felt that TPT biopsy may have a role in primary biopsy.

Key Words: Transrectal prostate biopsy, Transperineal prostate biopsy, Prostate biopsy

Core tip: Transperineal template biopsies are utilised in prostate cancer at an increasing rate instead of transrectal biopsies, yet there is no consensus on how this investigation should be utilised. Here we assess when this method of prostate biopsy is utilised, the number of biopsies that are taken and the method of transperineal template biopsy as well the likelihood of the increase in accuracy in diagnosing prostate cancer.

INTRODUCTION

Prostate cancer is now recognised as a major burden on the global health-care system. In the United States and in Europe, it is the most common neoplasm diagnosed in men and is responsible for 11% of all male cancer deaths[1,2]. After a diagnosis of prostate cancer is made, a number of treatments may be considered depending on the information provided by staging investigations. In patients who are thought to have organ confined prostate cancer, treatment options include radical prostatectomy, external beam radiation therapy, brachytherapy, focal treatment and active monitoring.

The main diagnostic tools utilised for a diagnosis of prostate cancer are digital rectal examination (DRE), serum concentration of Prostate Specific Antigen (PSA) and transrectal ultra sound guided (TRUS) biopsy. Prostate cancer can be detected by DRE alone in patients irrespective of the PSA reading[3]. A suspicious DRE is associated with more aggressive prostate cancer once diagnosed following biopsy[4] with the chance of having malignancy at biopsy higher in those with a suspicious DRE[5].

PSA measurement is now standard practise in prostate cancer diagnosis[6,7] since its first discovery as a serum marker for prostate cancer[8] having been demonstrated to be an independent predictor of cancer in comparison to a suspicious DRE or TRUS[9].

It is felt that performing biopsies under ultrasound guide where a transrectal approach is used for most biopsies is the standard. This is guided by hypoechoic areas in the peripheral zone but this is not always seen as Gray-scale TRUS does not detect areas of malignancy with adequate reliability[10] and as a consequence performing biopsies on only those areas that are hypoechoic would lead to cancers being missed[11] and has led to systematic biopsies being performed[11].

Pathological studies have demonstrated that prostate cancer can be a unifocal and unilateral disease[12] leading to a growing demand for minimally invasive treatment modalities prompting research into focal therapies which allows treatment of the cancer focus and sparing of normal tissue and therefore preserving genitourinary function[13,14]. It is felt that transperineal template (TPT) biopsy has a higher detection rate not of only prostate cancer[15-25] but also of clinically significant prostate cancer[17-19,26-29], anterior cancers[30,31] and has a higher detection rate than TRUS in those with a normal DRE[32]. TPT has a slightly longer training time[33] but has been demonstrated to diagnose cancer in those that have undergone previous negative biopsies via TRUS[26,29,34-39]. TPT biopsies are directed longitudinally to the peripheral zone and anterior part of the prostate so they should detect more cancer than via TRUS[40]. It is felt that this may be due to the inclusion of lateral cores explaining the higher diagnosis rate. It has been demonstrated that TPT biopsies detected significant cancers in those that had undergone TRUS biopsies with earlier negative findings[26,29,34-39] whilst others have demonstrated no difference between TRUS and TPT[41-43].

NUMBER OF BIOPSIES

It is felt that TRUS sextant biopsies are inadequate compared to TPT[15,44] and this results in a significant difference in the detection rates of prostate cancer when compared to twelve biopsies via TRUS or TPT[45-47]. It is felt that sextant biopsies via TPT can be utilised but only in cases of an abnormal DRE or increased PSA otherwise twelve biopsies are required[48]. This also increases the accuracy in Gleason grade in comparison to the final pathology following surgery[49]. It has been suggested that performing twenty two biopsies via TPT may increase the diagnostic accuracy[34] especially for larger sized prostates[50] whilst eight peripheral cores are sufficient for prostate volumes < 30 cc[23]. Furthermore, there is evidence that eighteen biopsies should be utilised in certain situations[51]. It has been demonstrated that using thirty six biopsies via TPT has a better diagnostic yield of prostate cancer then twelve via TRUS in those with normal DRE[25] whilst fourteen biopsies maybe sufficient but there is a risk of missing cancers[52]. Others have suggested that utilising a brachytherapy template with a 5 millimetre grid to guide template biopsies allows the detection of clinically significant prostate cancer[19] and that the volume of the prostate should be utilised as a guide to the number of biopsies with eight cores sufficient for small prostates and more extensive biopsies utilised for larger prostates[23] whereas it is felt that twelve biopsies are sufficient utilising a fan technique[17]. Clearly, larger prostates require higher numbers of biopsies for representative sampling.

Magnetic resonance imaging (MRI) has been demonstrated to have a high degree of accuracy in the detection of clinically significant prostate cancer when compared to radical prostatectomy specimens[53]. This has led to reports that MRI guided TRUS biopsies increase the detection of prostate cancer[54,55] as well as the detection of significant disease[56] with the possibility of utilising less biopsies[57,58]. However, MRI guided biopsy is not a modality that is utilised on a regular basis at the present time.

SATURATION BIOPSIES

In cases where saturation biopsies are utilised for investigation for previous negative biopsies with TRUS, it has been demonstrated that the detection rate can increase between 30%-40% using TRUS saturation biopsies, with the majority of these diagnoses being minimally differentiated disease[59-61]. Furthermore, there is an increase of 38% detection rate by TPT saturation biopsies after previous negative TRUS biopsies suggesting no advantage of TPT saturation biopsies over TRUS saturation biopsies[41,62]. Others have demonstrated that saturation biopsies do increase the detection rate of prostate cancer in those with previous negative biopsies with TRUS but have recommended that saturation biopsies should not be utilised as an initial strategy[63].

PREPARATION

As the TPT approach does not pass through the rectum it should be considered a sterile approach and therefore antibiotics should be recommended for those patients at a high risk of infection. There is little work looking at the role of antibiotics in the setting of TPT and yet many reports of TPT utilise antibiotics on a standard basis[17,23] which can be of concern given the prevalence of antibiotic resistance.

Bowel preparation is common amongst many urologists prior to TPT[64] as is felt that it reduces bacterial load[65] but given that TPT is a sterile procedure, the role of preventing infection may not be appropriate but it is felt that removing faecal material may improve the image of the prostate[66].

COMPLICATIONS

TPT is more invasive, has resource implications[19,67,68] as well as being associated with more complications thought to be as a result of increased number of biopsies being utilised[28,69,70]. There has been no difference in the complication rates following baseline TRUS or TPT[15,23,26,29,41,71-73], even in those that are thought be at increased risk of sepsis undergoing a biopsy via TPT as the primary choice[29] whilst it has been reported that there is a higher rate of urinary retention following saturation biopsies with TPT[62]. This maybe the result that some TPT biopsy cores go through the external urethral sphincter. Where saturation biopsies are to be utilised with TRUS, then the cost implications are similar to TPT as both would require anaesthesia as well as post procedure recovery.

CONCLUSION

Prostate biopsy plays a very important role in the diagnosis of prostate cancer. As prostate cancer is multifocal, it is felt that the detection rate may differ with the number of biopsies and biopsy method.

It has been suggested that TPT biopsies may have a lower rate of sepsis than TRUS and should not be used for only those undergoing a repeat biopsy but in all those in whom a biopsy is indicated[73]. Some authors have demonstrated no difference in detection rates, others have demonstrated a significant difference in the detection of clinically relevant disease and this is the group that it is often difficult in terms of management. Furthermore, this is the group that would benefit the most in terms of appropriate therapy. Those on active surveillance had their disease up-staged following TPT[74] and therefore any additional information in terms of Gleason grade would prove most useful to help plan treatment in this group.

Some issues needs to be addressed in terms of TPT biopsies. There is still not much information regarding the ideal number of biopsies that should be performed using this method and a consensus needs to be agreed upon this number as a significant difference in detection rates has been demonstrated when eighteen biopsies were taken in comparison to six-twelve via TPT[75], suggesting that prostate size should be utilised to decide the ideal number of biopsies[19,23]. The complication rates have been demonstrated to correlate with increased number of biopsies[76] and therefore it is suggested that twelve biopsies are sufficient[17]. Furthermore, despite evidence that TPT biopsies offer a higher diagnostic yield than TRUS, this could be secondary just due to the fact that more biopsies are taken at the time of TPT than TRUS. It is agreed that TPT biopsies are useful in those where previous biopsies have been negative and therefore may aid in the diagnosis in these patients[32,34,39].