Discrepancies between Gleason scores of needle biopsy and radical prostatectomy specimens

The purpose of this study was to determine the accuracy of Gleason scores in prostate needle biopsy diagnosis and to investigate factors affecting the accuracy of the tumor grade. A single pathologist reviewed 116 sets of prostate cancer biopsies and radical prostatectomy specimens. The following factors were examined to determine their effect on the accuracy of the biopsy Gleason scores: (i) relative tumor differentiation; (ii) pathological stage; (iii) amount of tissue in the biopsy specimen; (iv) amount of cancer tissue in the biopsy specimen; (v) tumor heterogeneity; (vi) clinical findings (prostate specific antigen value and digital rectal examination); and (vii) interobserver variability. In 53 cases the Gleason score of biopsy specimens was identical to the score of prostatectomy specimens (45.7%). Fifty-four cases (46.6%) of biopsy specimens were undergraded. The most common discrepancy was diagnosis of well-differentiated carcinoma in the biopsy but diagnosis of moderately differentiated tumor in the corresponding prostatectomy specimen. This discrepancy occurred when the amount of tumor in the biopsy was 3 mm or less. Biopsy and prostatectomy results showed less agreement when the original biopsy tumor grade rendered by nine different pathologists was used, suggesting that interobserver variability can adversely affect the accuracy of tumor grade. Clarifying the histologic criteria for distinguishing each grade, especially between Gleason grades 2 and 3, is important for accurate grading.     

Errors in histological grading by prostatic needle biopsy specimens: frequency and predisposing factors

Sampling error is an inherent problem of prostate biopsy. Consequently, there are problems in determining whether a given carcinoma is clinically significant on the basis of biopsy results. This study assesses the factors that predispose to errors in biopsy grading, as well as the dimensions of sampling error due to these factors. Among 187 cases, biopsy grading error was retrospectively related to grade heterogeneity in the prostate and to biopsy-related factors. Clinically relevant biopsy grading errors occurred in a quarter of the cases. Of all grading errors, at least 17% resulted from misinterpretation by the pathologist only. Overall, prostates with grade heterogeneity revealed grading errors twice as frequently as specimens without grade heterogeneity. In most cases, however, grading error resulted from multiple factors, such as the number and length of cores obtained (p<0.05). This was an important finding because the mean core length was only 9.4 mm, whereas the biopsy needle is designed to obtain cores of 15 mm. Moreover, clinically relevant biopsy grading error had occurred in almost half of the cases when the Gleason score was based on a tumour deposit measvring less than 0.5 mm (p<0.05). The clinical consequences of these findings are important. Clinicians should try to obtain at least six biopsies, each 15 mm in length, to minimize grading error. Pathologists should be cautious in reporting Gleason scores based on tumour lesions smaller than 400x total magnification field. Interpretation could be refined, when necessary, by warning the urologist of the Limitations of the biopsy report.     

Transition zone carcinoma of the prostate gland: a common indolent tumour type that occasionally manifests aggressive behaviour

AIMS: Tumours arising in the transition zone (TZ) of the prostate gland are often well differentiated and considered clinically unimportant. We have observed examples of high-grade TZ cancers that prompted this study. METHODS: Review of 654 radical prostatectomy specimens previously assessed by systematic whole organ histology identified 187 (29%) TZ cancers of which 76 (11.6%) represented the index (main) tumour. These were compared with a volume-matched group of 76 peripheral zone (PZ) carcinomas. RESULTS: Fifty-nine of 76 TZ index carcinomas had additional minor tumours mainly located in the PZ. Compared to PZ tumours of similar size, TZ tumours had significantly lower Gleason scores, less Gleason grade 4/5 and lower rates of capsular penetration and positive surgical margins. However, within this TZ tumour group, seven carcinomas had a major Gleason grade 4 or 5 component with high rates of capsular penetration (57%) and positive surgical margins (43%). Positive anterior and bladder neck margins were more common in TZ carcinoma than peripheral tumours and transperineal biopsy was the method of choice for TZ cancer diagnosis. CONCLUSIONS: A subset of TZ carcinoma characterised by high tumour grade has a significant risk of extraprostatic spread, margin positivity and possible biochemical failure. We recommend transperineal prostate biopsy for TZ tumour diagnosis and histological sampling of the anterior TZ at radical prostatectomy, even if macroscopically normal, to detect patients at risk from aggressive TZ carcinoma.     

What is the consistency between the results of needle biopsy and prostatectomy specimen pathology results? A pilot study

Background/aim The aim of this study was to establish the relationship between the needle biopsy and the pathology result after radical prostatectomy administrated for prostate cancer. Materials and methods We retrospectively analyzed 67 patients who had undergone radical prostatectomy from 2016 to 2019. All surgeries and all biopsies were performed in the third author’s urology department. Samples were collected through 12-core biopsy under local anesthesia. All specimens were studied in the pathology department of the third author’s center. The results evaluated were needle biopsies’ Gleason scores and prostatectomy specimens’ Gleason scores.Results Inclusion criteria were not having any neo-adjuvant treatment and being treated with surgery after needle biopsy. Gleason scores obtained from needle biopsies and prostatectomy specimens were evaluated. The comparison revealed that 39% of the tumors were undergraded, 7% were overgraded, and 54% had exact scoring in needle biopsies and prostatectomy specimens according to the detailed Gleason scoring as primary and secondary metrics. The patients were grouped into five categories according to the ISUP 2014 prostate cancer grading system. The relationship was strong with 64% of results staying in the same group after the operation; nevertheless, the correlation remained weak based on the kappa coefficient. Conclusion The information obtained from the needle biopsy is not a strong herald of the pathological result. Urologists should have awareness of this restraint when utilizing the needle biopsy’s Gleason score in decision making and treatment planning.     

Invasion of fat justifies assignment of stage pT3a in prostatic adenocarcinoma

AIMS: The detection of invasive cancer cells within the adipose tissue of needle biopsies has been regarded as bona fide evidence of extraprostatic tumour extension, and as a consequence may influence subsequent patient management. However, the identification of rare intraprostatic fat from recent reports involving series of autopsies has challenged this practice principle. We examined totally embedded, whole-mounted radical prostatectomy specimens in order to determine the occurrence of intraprostatic fat in prostatic tissue, and further, to assess the importance of the identification of fat infiltration by neoplastic cells in needle biopsy specimens as a marker of extraprostatic infiltration by tumour. METHODS: Between 2000 and 2003, 313 consecutive patients underwent radical prostatectomy for clinically localised prostate cancer in the Indiana University Hospital. All radical prostatectomy specimens were completely embedded and whole mounted for histological examination. All slides were reviewed and evaluated for the presence or absence of intraprostatic fat. Other pathological characteristics of prostate cancer were also assessed and clinical data were gathered by a review of patient charts. RESULTS: The mean age of patients was 60 years. None of these 313 radical prostatectomy specimens revealed any adipose tissue components within the most peripheral boundary of normal prostatic acini in the prostate. CONCLUSIONS: We found no evidence of intraprostatic fat and our findings suggest that, at best, the occurrence of fat within the prostate is of extreme rarity. Accordingly, the finding of carcinoma invading adipose tissue in needle biopsies should continue to be considered as extraprostatic extension and stage pT3a assigned.     

Therapy-associated effects in the prostate gland

Diverse therapies are used to treat both benign prostatic hyperplasia and adenocarcinoma. Transurethral resection, a common surgical procedure, may give rise to characteristic necrobiotic granulomas that manifest in subsequent pathology samples. Radiation and hormone therapy have traditionally been used in prostatic adenocarcinoma. Morphological effects are often identified in needle biopsy specimens, transurethral resectates, and radical prostatectomy specimens. A range of histological changes are noted in the non-neoplastic prostate tissue, as well as in the pre-neoplastic and carcinomatous areas. Other ablative therapies, such as cryotherapy, and emerging focal therapies, including high-intensity focused ultrasound, photodynamic therapy, and interstitial laser thermotherapy, may have morphological effects on prostate tissue. It is important for the pathologist to be aware of the spectrum of histological changes affecting the prostate gland post-therapy. The treatment effects may obscure residual carcinoma, and make measurements of tumour extent and stage difficult. Furthermore, some therapies can profoundly alter the neoplastic glands to such an extent that Gleason scoring is no longer valid. As new therapies are developed for prostate cancer, it is important to document their effects on benign and malignant prostate tissue and to understand possible implications for traditional prognostic factors, especially Gleason grade.     

Analysis of Gleason grade and scores in 90 Nigerian Africans with prostate cancer during the period 1994 to 2004

Objectives

To determine the relative frequency of prostate cancer among surgical specimens, and among prostate specimens received at the pathology department ,University Hospital Calabar.

Methods

Histology records were reviewed for the following: total number of histology specimens received; total number of prostate specimens; total number of prostate cancer; and the total number of cancers in males during the study period. Histology sections 4–5microns thick were cut from paraffin blocks and stained by Haematoxylin and Eosin (H&E). Histopathologic specimens were classified using the grading system of tumour differentiation described by Gleason and associates.

Results

One hundred and twenty three cancers of the prostate were received, constituting 2% of the total surgical specimens and 31% of prostate specimens. Thirty three cases (27%) could not be analyzed; therefore the study is based on 90 prostate cancer specimens. Eighty nine (99%) cases were epithelial tumours (adenocarcinoma.) There was a single mesenchymal tumour (rhabdomyosarcoma) (1%). The commonest grade in this study was the high grade (Gleason grade IV).

Conclusions

We observed that prostate cancer is a common among males (all sites) diagnosed at the University Hospital Calabar, with a peak incidence between the ages of 61 – 70 years (seventh decade).     

Defining clinically significant prostate cancer on the basis of pathological findings

The definition of clinically significant prostate cancer is a dynamic process that was initiated many decades ago, when there was already evidence that a great proportion of patients with prostate cancer diagnosed at autopsy never had any clinical symptoms. Autopsy studies led to examinations of radical prostatectomy (RP) specimens and the establishment of the definition of significant cancer at RP: tumour volume of 0.5 cm³, Gleason grade 6 [Grade Group (GrG) 1], and organ‐confined disease. RP studies were then used to develop prediction models for significant cancer by the use of needle biopsies. The first such model was used to delineate the first active surveillance (AS) criteria, known as the ‘Epstein’ criteria, in which patients with a cancer Gleason score of 3 + 3 = 6 (GrG1) involving fewer than two cores, and <50% of any given core, and a prostate‐specific antigen density of <0.15 ng/ml per cm³ had a minimal risk of significant cancer at RP. These were adopted as components of the ‘very‐low‐risk category’ of the National Comprehensive Cancer Network guidelines, in which AS is supported as a management option. With the increase in the popularity of AS, much research has been carried out to better define significant/insignificant cancer, in order to be able to safely offer AS to a larger proportion of patients without the risk of undertreatment. Research has focused on allowing higher volume tumours, focal extraprostatic extension, and a limited amount of Gleason pattern 4, and the significance of different morphological patterns of Gleason 4. Other areas of research that will probably impact on the field but that are not covered in this review include the molecular classification of tumours and imaging techniques.     

Molecular analysis of multifocal prostate cancer lesions

To analyse the origin of multifocal prostate cancer lesions, radical prostatectomy specimens from 17 patients were examined. As a marker of genetic lineage, the allelotype based on 33 microsatellite loci was compared between the different tumours present in a given case. Some results provide evidence suggestive of a clonal origin of multiple tumours in a subset of the prostates. In five cases, for example, comparison of multifocal tumour lesions within a given case revealed at least two concordant changes in allelic imbalance (AI) sequence dosages at different loci. In addition, considerable heterogeneity of allelotype was found within and among tumour foci of a given case. In five of the six tumours analysed for intratumour heterogeneity, for example, more than five discordant AI changes were found in one tumour region but not in the other. Conclusions regarding the clonality of such heterogeneous lesions are difficult to draw. A high frequency of AI changes in four lesions exhibiting prostatic intraepithelial neoplasia (mean 6·5 changes per lesion, range 3–6) was found, compared with eight primary tumours present in the same cases (mean 5·8 changes per lesion, range 3–6). The interpretation of AI associated with clinically detected prostate cancer remains a highly complex issue. The fact that no clear evidence was obtained for either a clonal or a non-clonal origin of multiple lesions in a given prostate indicates that several different mechanisms are likely to operate in establishing the allelotype and that additional evidence from unique mutations or selective gene inactivation may be necessary to obtain definitive results. Copyright © 1999 John Wiley & Sons, Ltd.     

Preoperative prediction of Gleason grade in radical prostatectomy specimens: the influence of different Gleason grades from multiple positive biopsy sites.

The Gleason score of prostate adenocarcinomas is an important preoperative predictor of cancer behavior, and is used to help guide treatment. In the setting of more than two positive biopsy sites, pathologists usually grade the tumor at each site separately, and the Gleason score may differ from each positive site. This study seeks to determine if the highest Gleason score in all biopsy sites, or the Gleason score in the site with the highest tumor volume on the needle biopsy is the best predictor of final Gleason score in the radical prostatectomy specimens. Various preoperative biopsy findings were analyzed. All 151 patients had at least two positive biopsy sites and underwent radical prostatectomy. Primary and secondary Gleason pattern grades were assigned for each positive biopsy site. The tumor volume in the needle biopsy site was defined by the percentage of areas of biopsy cores involved by cancer. The radical prostatectomy specimens were completely embedded and processed in the whole-mount method. The Gleason score from both the biopsy site with the highest Gleason score and the biopsy site with the highest tumor volume on the needle biopsy correlated equally well with final Gleason score at radical prostatectomy (Spearman correlation coefficient =0.54 for both, P<0.001). The Gleason score from both the biopsy site with the highest Gleason score and the biopsy site with the highest tumor volume on the needle biopsy also correlated with primary Gleason pattern grade at radical prostatectomy (Spearman correlation coefficient =0.53 for both, P<0.001). Secondary Gleason pattern grade from the biopsy site with the highest tumor volume on the needle biopsy correlated with secondary Gleason pattern grade at radical prostatectomy slightly better than those from the biopsy site with the highest Gleason score (Spearman correlation coefficient, 0.32 vs 0.24; both P<0.001). Our data indicate that the highest Gleason score from all sites and the Gleason score from the site with the highest tumor volume on the needle biopsy are equally and significantly predictive of final Gleason score on radical prostatectomy. Both methods of prediction are significantly predictive of primary and secondary Gleason pattern grade on radical prostatectomy. We recommend that the highest Gleason score from all positive biopsy sites should be used when assigning an initial score using needle biopsies.     

Is it possible to predict low‐volume and insignificant prostate cancer by core needle biopsies?

In an attempt to minimize overtreatment of localized prostate cancer (PCa) active surveillance (AS) and minor invasive procedures have received increased attention. We investigated the accuracy of pre‐operative findings in defining insignificant disease and distinguishing between unilateral/unifocal and bilateral/multifocal PCa. One‐hundred and sixty patients undergoing radical prostatectomy were included. Histology reports from the biopsies and matching prostatectomies were compared. Three definitions of insignificant cancer were used: InsigE: tumour volume ≤0.5 mL; InsigW: tumour volume ≤1.3 mL; InsigM: tumour ≤5% of total prostate volume and prostate‐specific antigen (PSA) ≤10 ng/mL. In all definitions, Gleason score (GS) was ≤6 and the tumour was organ confined. Biopsies alone performed poorly as a predictor of unifocal and unilateral cancer in the prostatectomy specimens with positive predictive values of 17.8% and 18.9% respectively. Inclusion of other clinical and biochemical parameters did not significantly increase the predictive value. However, the combination of GS ≤ 6, PSA ≤ 10 ng/mL and unifocal or unilateral cancer in biopsy cores resulted in a positive predictive value of 61.1%, 38.9% and 12.0%, respectively, for identifying InsigM, InsigW and InsigE in the prostate specimen. Conclusively, routine prostate biopsies cannot predict unifocal and unilateral PCa, and must be regarded insufficient to select patients for focal therapy. Although candidates for AS may be identified using standard biopsies, a considerable fraction of patients will be understaged. There is a need for more precise diagnostic tools to assess intraprostatic tumour growth.     

MRI-targeted prostate biopsy: key considerations for pathologists

We discuss the role of the pathologist for MRI-targeted prostate biopsy with a focus on specimen processing, reporting of pathological findings and quality assurance in establishing a successful MRI-targeted biopsy programme. The authors discuss the current issues relevant to pathologists regarding MRI-targeted prostate biopsy. In addition, a brief review of the recently published literature was performed using an English literature search on PubMed with a focus on original investigations related to MRI-targeted prostate biopsy. Our search terms included the following: ‘prostate cancer’, ‘pathology’, ‘histology’, ‘reporting’, ‘cores’, ‘imaging’, ‘MRI’ and ‘mpMRI’. Prostate multiparametric magnetic resonance imaging (mp-MRI) and MRI-targeted biopsy has been shown to improve the diagnosis of clinically significant prostatic adenocarcinoma and can affect the management of patients with prostate cancer. The current active surveillance guidelines were based on data from TRUS biopsies and not MRI-targeted biopsies. MRI-targeted biopsy acquires multiple cores of tissue from one or more suspicious lesions found on mp-MRI. The way in which multiple targeted core biopsies obtained from a single image-directed region of interest are analysed and reported can potentially alter the Gleason score and tumour burden as reported on biopsy, which could undoubtedly alter patient management. Pathologists play an important role in the reporting of MRI-targeted prostate biopsies. How we report prostate cancer grade and extent on these biopsies can influence patient management. In addition, the pathologist should be involved in the quality assurance for patients undergoing MRI-targeted prostate biopsy.     

Observer variation in the histological grading of rectal carcinoma.

The variation between two observers in grading 100 biopsies and the corresponding main specimens of rectal carcinomas has been examined. Using kappa statistics, which take account of chance agreement, we found a highly significant level of agreement. As expected, higher levels were obtained for intraobserver agreement. However, disagreements between observers were in many instances "haphazard" and there were differences in bias between them. Fifty paired biopsies and main tumours were graded by five observers and the results analysed for bias and by kappa statistics for overall and conditional agreement. These methods revealed significant overall agreement but the levels for some observer pairs did not differ significantly from chance. Examination for observer bias indicated differing standards of grading, and haphazard disagreements reached high levels for some observer pairs. The intraobserver agreement between the grade of the biopsy and the corresponding main tumour varied from 56-69% but only 52% of the poorly differentiated tumours were diagnosed as such in the preoperative biopsy by the "specialist" observer. The poor predictive value was not improved by taking multiple biopsies. We conclude that the grade of a rectal carcinoma cannot be accurately assessed on a preoperative biopsy and that this has serious implications for the management of low rectal cancers. Furthermore the wide discrepancies in diagnostic standards between some pathologists mean that studies on the treatment and prognosis of rectal cancer which utilise histological grade for comparison purposes must be viewed with considerable skepticism.     

Current practice of Gleason grading of prostate carcinoma

The Gleason grading system remains one of the most powerful prognostic factors in prostate cancer and is the dominant method around the world in daily practice. It is based solely on the glandular architecture performed at low magnification. The Gleason grading system should be performed in needle core biopsies and radical prostatectomy specimens where it shows a reasonable degree of correlation between both specimens, and most importantly, it remains vital in the treatment decision-making process. This review summarizes the current status of Gleason grading in prostate cancer, incorporating recent proposals for the best contemporary practice of prostate cancer grading.     

Ki67 LABELLING INDEX: AN INDEPENDENT PREDICTOR OF PROGRESSION IN PROSTATE CANCER TREATED BY RADICAL PROSTATECTOMY

The clinical course of prostate cancer is highly variable and cannot satisfactorily be predicted by histological criteria alone. Both tumour cell proliferation and neuroendocrine differentiation have been suggested as additional prognostic parameters, neuroendocrine differentiation being considered to enhance tumour cell proliferation. This study investigated the prognostic value of tumour cell proliferation [Ki67 labelling index (LI), MIB 1] and neuroendocrine differentiation and their relationship to each other. One hundred and thirty-seven paraffin-embedded radical prostatectomy specimens were examined. Neuroendocrine differentiation was found in 58 per cent of cases, but was not associated with pTN stage, Gleason score, Ki67 LI, or tumour progression. Ki67 LI was not significantly associated with pTN stage or with Gleason score. High grade ( P =0·0005), advanced local stage ( P =0·0004), positive lymph nodes ( P =0·02), and high Ki67 LI ( P =0·0203) were predictors of tumour progression if univariate analysis was performed, but Cox stepwise regression showed that only advanced local stage ( P =0·0025) and Ki67 LI ( P =0·0105) were independent predictors of tumour progression, the relative risk being 3·6 and 2·5, respectively. It is concluded that Ki67 is an important prognostic marker in prostate cancer with a potential for routine application.     

Numerical chromosomal aberrations in prostate cancer: correlation with morphology and cell kinetics

Eleven routinely processed radical prostatectomy specimens were studied for the presence of numerical chromosomal aberrations by means of in situ hybridization with nucleic acid probes specific for chromosomes 7, 10, 17, X, and Y. Cytogenetic information was correlated with morphology, tumour stage and volume as well as with cell kinetics, the latter being assessed by immunohistochemistry with antibodies raised against the proliferative cell nuclear antigen (PCNA) and against a formalin-resistant epitope of the Ki-67 antigen, MIB 1. In 5 of 11 cases, numerical aberrations of at least one chromosome were found. The cases with normal chromosome numbers were those with the smallest volumes of Gleason grade 4 and/or 5 tumour (mean 0.5 cm³) and represented tumours restricted to the prostate. Tumours with aberrations in the number of detected chromosomes showed advanced stages and large volumes of high-grade tumour (mean 12.5 cm³). All 4 tumours with positive surgical margins were recruited from a group with marked local heterogeneity in chromosome numbers. Immunostaining with MIB 1 and PCNA was most intense in areas of high-grade tumour and was positively correlated with the emergence of chromosomal aberrations. The data suggest that the appearance of numerical chromosomal aberrations in prostate cancer coincides with aggressive tumour behaviour and could be used as an additional prognostic marker.This work is part of E.K.'s doctoral thesis     

Early prostate cancer detected using expression of non-functional cytolytic P2X7 receptors

AIMS: To detect early prostate cancer reliably by monitoring the expression of non-functional P2X(7) cytolytic purinergic receptors. METHODS AND RESULTS: P2X(7) receptors were absent from normal prostate epithelium obtained from post mortem tissue and tissue from cases of transurethral resection collected from young men (n = 23) who were confirmed to be free of cancer at later procedures 5-10 years after collection of the original samples. However, P2X(7) was present in every case of 116 confirmed prostate cancers regardless of Gleason grade or patient age. P2X(7) was present in apparently normal epithelial cells in acini well outside the tumour margins, but appeared in a distinct stage-specific manner commencing with the nucleus, progressing to the cytoplasm and collecting finally on the apical membrane of the epithelial cells in morphologically distinct cancer. The pattern of P2X(7) receptor localization in the epithelial cells was recorded in earlier biopsies obtained from the same patient cohort. One hundred and fourteen of 116 prostates stained positively for P2X(7) at the earliest biopsy, though generally with a less advanced pattern of distribution. CONCLUSIONS: The appearance of P2X(7) receptors in normal prostate tissue adjacent to prostate tumours makes direct tumour biopsy less critical for positive cancer diagnosis and enables cancer progression to be monitored.     

Bench to bedside: research influencing clinical practice in prostate pathology

Prostate cancer is biologically heterogeneous ranging from clinically indolent disease that “old men die with” to aggressive tumours that metastasise and cause death. Optimal management of this disease requires accurate prognostication to avoid over-treatment of the former and prompt appropriate treatment of the latter. Prognostication of prostate cancer is challenging as tumour is often not well visualized on radiological examination, is often detected in non-targeted systematic biopsies and cannot be subjected to a wide local excision for detailed histological examination. Several histopathological parameters that aid risk stratification of prostate cancer have been identified but some tumours lacking adverse pathology findings exhibit aggressive behaviour. Tissue biomarkers could improve the accuracy of prognostication of prostate cancer. This review outlines how histopathological research has impacted the diagnosis, prognostication, and treatment of prostate cancer. We also highlight limitations of the current evidence base and outline the role of the practicing histopathologist in optimizing the clinical utility of biomarker assays.     

VERDICT MRI validation in fresh and fixed prostate specimens using patient‐specific moulds for histological and MR alignment

The VERDICT framework for modelling diffusion MRI data aims to relate parameters from a biophysical model to histological features used for tumour grading in prostate cancer. Validation of the VERDICT model is necessary for clinical use. This study compared VERDICT parameters obtained ex vivo with histology in five specimens from radical prostatectomy. A patient‐specific 3D‐printed mould was used to investigate the effects of fixation on VERDICT parameters and to aid registration to histology. A rich diffusion data set was acquired in each ex vivo prostate before and after fixation. At both time points, data were best described by a two‐compartment model: the model assumes that an anisotropic tensor compartment represents the extracellular space and a restricted sphere compartment models the intracellular space. The effect of fixation on model parameters associated with tissue microstructure was small. The patient‐specific mould minimized tissue deformations and co‐localized slices, so that rigid registration of MRI to histology images allowed region‐based comparison with histology. The VERDICT estimate of the intracellular volume fraction corresponded to histological indicators of cellular fraction, including high values in tumour regions. The average sphere radius from VERDICT, representing the average cell size, was relatively uniform across samples. The primary diffusion direction from the extracellular compartment of the VERDICT model aligned with collagen fibre patterns in the stroma obtained by structure tensor analysis. This confirmed the biophysical relationship between ex vivo VERDICT parameters and tissue microstructure from histology.