Abstract
For decades, the stiffness difference detected using digital rectal examination (DRE) has been a useful technique for suspecting Prostate cancer (PCa). However, the ability of DRE alone for detecting PCa remains poor. Cancerous tissues tend to be stiffer than the adjacent normal tissues, and the biophysical and biochemical properties of the tumour microenvironment (TME) are different from those of normal tissues. The alteration of matrix stiffness is an immediate effect of contractility-driven Extracellular matrix (ECM) re-modelling, and tissue elasticity is a result of increased cell density and collagen formation, hence changes in elasticity can indicate an abnormal pathological mechanism.The ability to detect tissue elasticity accurately and early can lead to a more reliable diagnosis and prognosis of diseases. Ultrasound shear wave elastography (USWE) is a promising imaging technique that measures tissue modulus and is increasingly applied for cancer detection. In this thesis, the first and second studies were to assess the application of both multiparametric magnetic resonance imaging (mpMRI) and USWE in precisely determining the size of PCa lesions, and the correlation of quantitative tissue stiffness measurements obtained by USWE with Prostate Imaging-Reporting and Data System (PI-RADS) scoring of mpMRI using Gleason scores (GS) of radical prostatectomies as a reference standard. 3D-printed patient-specific moulds were used to guide histopathology radical prostatectomy. The first study population included 202 men with clinically localized PCa opting for radical surgery. A significant number of men had underestimation of PCa using mpMRI (82.1%; 87/106) or USWE (64.6%; 62/96). On average tumour size was underestimated by a median size of 7mm in mpMRI, and 1mm in USWE. There were 327 cancerous lesions (153 for mpMRI and 174 for USWE). mpMRI and USWE underestimated the majority of cancerous lesions (108/153; 70.6%) and (88/174; 50.6 %) respectively. Validation cohort data confirmed these findings mpMRI had a nearly 20% higher underestimation rate than USWE (χ2 (1, N= 327) = 13.580, p= 0.001); especially in the mid and apical level of the gland. Clinically non-significant cancers were underestimated in significantly higher numbers in comparison to clinically significant cancers. Size measurement of prostate cancers on preoperative imaging utilising maximum linear extent technique, underestimated the extent of cancer. PCa size measurements irrespective of location within the gland or clinical significance are significantly underestimated by both imaging modalities in men undergoing radical prostatectomy.
The second study included 196 men with localised PCa who were prospectively recruited into the study and had quantitative prostate tissue stiffness measurements in kilopascals (kPa) using transrectal USWE prior to radical prostatectomy. PI-RADS scores of mpMRI were also obtained in all the men. Imaging and histopathology of radical prostatectomy specimens were oriented to each other using patient-specific customised 3D moulds to guide histopathology grossing of radical prostatectomy specimens. All included patients had confirmed PCa on Transrectal ultrasoundguided prostate biopsy (TRUS-PBX), had both USWE and mpMRI imaging data and underwent radical prostatectomy. Chi-square test with a 95% confidence interval was used to assess the difference between GS of radical prostatectomy and PI-RADS classification, as well as GS of radical prostatectomy and stiffness in kPa using USWE. The correlation coefficient (r) was calculated in order to investigate the relation between PI-RADS classification and tissue stiffness in kPa. There was a statistically significant correlation between USWE-measured tissue stiffness and GS (χ2 (2, N = 196) = 23.577, p < 0.001). Also, there was a statistically significant correlation between GS and PIRADS score (χ2 (2, N = 196) = 12.838, p = 0.002). High PI-RADS on mpMRI and high stiffness on USWE (> 100 kPa) detected more than 80% and 90% high risk PCa disease. However, a weak correlation coefficient of 0.231 was observed between PI-RADS score and level of tissue stiffness measured in kPa.
PCa has a poor prognosis and high mortality rate due to metastases. Why do some cancers with similar GS metastasize whereas others behave in a more indolent way? ECM remodelling and stroma composition have been linked to cancer progression including key components of cell migration, tumour metastasis, and tissue stiffness. Moreover, collagens and cancer-associated fibroblasts (CAFs) are two of the most significant components of the ECM and have been ascribed to many aspects of neoplastic transformation.
The third objective was to investigate the correlation between the immunohistochemistry (IHC) and genomics characterisation of CAFs in the PCa TME and transrectal USWE measured tissue stiffness in men with clinically localised PCa. Thirty patients with clinically localised PCa undergoing radical prostatectomy for different risk categories of tumour (low, intermediate, and high) defined by GS were prospectively recruited into this study. Prostatic tissue stiffness was measured using USWE prior to surgery. The CAFs within the TME were identified by IHC using a panel of six antibodies (FAP, SMAα, FSP1, CD36, PDGFR α and β) as well by gene expression profiling using tempO-sequence analysis. The pattern and degree of IHC positivity (measured by Quick score method and evaluated by the ImageJ) and expression of genes characterising CAFs were then correlated with USWE measured tissue stiffnesses using the spearman rank correlation and person correlation. There was a statistically significant correlation between GS of cancers, the pattern of staining for CAFs by IHC staining, and tissue stiffness measured in kPa using USWE (p <0.001). Significant differences were also observed in IHC staining patterns between normal prostatic tissues and cancerous prostatic tissues. PDGFRβ and SMAα immunostaining scores increased linearly with increasing the USWE stiffness and the GS of PCa. There was a significant positive correlation between increasing tissue stiffness in tumour fibromuscular stroma and the gene expression of SMAα and PDGFRβ gene expression in the fibromuscular stroma, (p < 0.001). USWE measured tissue stiffness correlates with increased SMAα and PDGFRβ expressing CAFs and PCa GS. This mechanistic correlation could be used for predicting the upgrading of GS from biopsies to radical surgery and response to novel treatments.
The last objective of this thesis was to characterise collagen re-modelling around localised PCa using the second harmonic generation (SHG) of collagen and compared this with USWE measured stiffness in men with clinically significant prostate cancer (csPCa). TempO-sequence assay for gene expression of COL1A1 and COL3A1 was used to confirm the expression of collagen in peritumoural matrix. SHG imaging and genotyping of ECM around PCa showed changes in content, orientation, and type of collagen according to Gleason grades (cancer aggressivity) and this correlated with tissue stiffness measured by USWE in kPa. Also, there were clear differences between collagen orientation and type around normal and cancerous tissues.
| Date of Award | 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Ghulam Nabi (Supervisor) & Chunhui Li (Supervisor) |