Bridging the gap between micro- and macro-scales in medical imaging with textural analysis - A biological basis for CT radiomics classifiers?

INTRODUCTION: Studies suggest there is utility in computed tomography (CT) radiomics for pancreatic disease; however, the precise biological interpretation of its features is unclear. In this manuscript, we present a novel approach towards this interpretation by investigating sub-micron tissue structure using digital pathology. METHODS: A classification-to attenuation (CAT) function was developed and applied to digital pathology images to create sub-micron linear attenuation maps. From these maps, grey level co-occurrence matrix (GLCM) features were extracted and compared to pathology features. To simulate the spatial frequency loss in a CT scanner, the attenuation maps were convolved with a point spread function (PSF) and subsequently down-sampled. GLCM features were extracted from these down-sampled maps to assess feature stability as a function of spatial frequency loss. RESULTS: Two GLCM features were shown to be strongly and positively correlated (r = 0.8) with underlying characteristics of the tumor microenvironment, namely percent pimonidazole staining in the tumor. All features underwent marked change as a function of spatial frequency loss; progressively larger spatial frequency losses resulted in progressively larger inter-tumor standard deviations; two GLCM features exhibited stability up to a 100 µm pixel size. CONCLUSION: This work represents a necessary step towards understanding the biological significance of radiomics. Our preliminary results suggest that cellular metrics of pimonidazole-detectable hypoxia correlate with sub-micron attenuation coefficient texture; however, the consistency of these textures in face of spatial frequency loss is detrimental for robust radiomics. Further study in larger data sets may elucidate additional, potentially more robust features of biologic and clinical relevance.

Impact of somatic molecular profiling on clinical trial outcomes in rare epithelial gynecologic cancer patients.

OBJECTIVES: Conducting clinical trials in rare malignancies is challenging due to the limited number of patients and differences in biologic behavior. We investigated the feasibility and clinical utility of using genomic profiling for rare gynecologic malignancies. METHODS: Rare epithelial gynecologic cancer patients were analyzed for somatic variants through an institutional molecular profiling program using the Sequenom MassArray platform or the TruSeq Amplicon Cancer Panel on the MiSeq platform. Clinical trial outcomes by RECIST 1.1, and time on treatment were evaluated. RESULTS: From March 2012 to November 2015, 767 gynecologic patients were enrolled and 194 (27%) were classified as rare epithelial malignancies. At least one somatic mutation was identified in 72% of patients, most commonly in TP53 (39%), KRAS (28%) and PIK3CA (27%). A total of 14% of patients were treated on genotype-matched trials. There were no significant differences in overall response rate between genotype-matched versus unmatched trials, nor in median time on treatment between genotype trials and the immediate prior systemic standard treatment. Among 13 evaluable Low Grade Serous ovarian cancer patients treated on genotype-matched trials with MEK inhibitor-based targeted combinations, there were four partial responses. CONCLUSIONS: Somatic molecular profiling is feasible and enables the identification of patients with rare gynecologic cancers who are candidates for genotype-matched clinical trials. Genotype-matched trials, predominantly MEK-based combinations in KRAS and/or NRAS mutant Low Grade Serous ovarian cancer patients, and genotype-unmatched trials, have shown potential clinical activity. Prospective trials with integrated genotyping are warranted to assess the clinical utility of next generation sequencing tests as a standard clinical application in rare malignancies.

Genotype-matched treatment for patients with advanced type I epithelial ovarian cancer (EOC).

BACKGROUND: Genomic alterations that activate the MAPK signaling pathway frequently occur in Type I Epithelial Ovarian Cancers (EOCs). We evaluated therapeutic response outcomes in patients with type I EOC treated with genotype-matched therapy on clinical trials enrolled in a prospective molecular profiling program. MATERIAL AND METHODS: Formalin fixed paraffin embedded tumor tissues were prospectively screened for genomic alterations using MALDI-ToF mass-spectrometry platform or targeted sequencing using the Illumina MiSeq TruSeq Amplicon Cancer Panel. Treatment outcomes on genotype-matched trials were retrospectively reviewed using RECIST version 1.1 and Gynecological Cancer Intergroup CA125 related-response criteria RESULTS: 55 patients with type I EOC underwent molecular profiling, 41 (75%) low grade serous (LGS), 9 (16%) clear cell (CC), and 5 (9%) mucinous (MC) histologies. Thirty-five patients (64%) were found to have ≥1 somatic mutations: 23 KRAS, 6 NRAS, 5 PIK3CA, 2 PTEN, 1 BRAF, 1 AKT, 1 TP53, and 1 CTNNB1. Fifteen patients were subsequently enrolled in genotype-matched phase I or II trials, including 14 patients with KRAS/NRAS mutations treated with MEK inhibitor targeted combinations. Among 14 RECIST evaluable patients, there were 7 partial responses (PR), 7 stable disease (SD) and 1 disease progression (PD). CA125 responses were observed in 10/10 evaluable KRAS/NRAS mutant patients treated with MEK inhibitor combinations CONCLUSIONS: Genotyping and targeted sequencing of Type I EOCs frequently identifies actionable mutations. Matched treatment with MEK-based combination therapy in KRAS and/or NRAS mutant type I EOC patients is an active therapeutic strategy.

Analysis of the intra- and intertumoral heterogeneity of hypoxia in pancreatic cancer patients receiving the nitroimidazole tracer pimonidazole.

BACKGROUND: Hypoxia is thought to be an adverse feature of pancreatic cancer, but direct measurement in patients is technically challenging. To address this, we characterised the intra/interpatient heterogeneity of hypoxia in surgical specimens from patients who received the 2-nitroimidazole tracer pimonidazole pre-operatively. METHODS: Pimondazole was given intravenously 16-20 h before pancreatectomy, and the extent and intratumoral heterogeneity of hypoxia determined by image analysis applied to multiple tissue blocks stained by immunohistochemistry. Intra/interpatient heterogeneity was estimated by variance component analysis. RESULTS: Pimonidazole staining was analysed in 10 tumours. The extent of labelling varied amongst patients (0-26%), with a broader range of hypoxia in the epithelial (1-39%) compared with the stromal (1-13%) compartments. Variance component analysis demonstrated greater inter- than intrapatient variability of hypoxia, and that multiple (4-5) tumour sections are required to provide a consistent evaluation of its extent in individual tumours. CONCLUSIONS: There is significant intra- and intertumoral heterogeneity of hypoxia in pancreatic cancers, and these do not appear to be generally more hypoxic than other cancer types. This study establishes the feasibility to assess hypoxia in pancreatic cancer patients using pimonidazole, but questions the reliability of measurements made using a single tissue section.

A phase II study of erlotinib in gemcitabine refractory advanced pancreatic cancer.

BACKGROUND: Erlotinib induced skin toxicity has been associated with clinical benefit in several tumour types. This phase II study evaluated the efficacy of erlotinib, dose escalated to rash, in patients with advanced pancreatic cancer previously treated with gemcitabine. METHODS: Erlotinib was given at an initial dose of 150 mg/day, and the dose was escalated by 50mg every 2 weeks (to a maximum of 300 mg/day) until >grade 1 rash or other dose limiting toxicities occurred. Erlotinib pharmacokinetics were performed, and baseline tumour tissue was collected for mutational analysis and epidermal growth factor receptor (EGFR) expression. The primary end-point was the disease control rate (objective response and stable disease >8 weeks). RESULTS: Fifty-one patients were accrued, and 49 received treatment. Dose-escalation to 200-300 mg of erlotinib was possible in 9/49 (18%) patients. The most common ⩾ grade 3 adverse events included fatigue (6%), rash (4%) and diarrhoea (4%). Thirty-seven patients were evaluable for response, and the best response was stable disease in 12 patients (32% (95% confidence interval (CI) 17-47%)). Disease control was observed in nine patients (24% (95% CI: 10-38%)). Median survival was 3.8 months, and 6 month overall survival rate was 32% (95% CI 19-47%). Mutational analysis and EGFR expression were performed on 29 patients, with 93% having KRAS mutations, none having EGFR mutations, and 86% expressing EGFR. Neither KRAS mutational status nor EGFR expression was associated with survival. CONCLUSIONS: Erlotinib dose escalated to rash was well tolerated but not associated with significant efficacy in non-selected patients with advanced pancreatic cancer.