Katie N. Hunt

Tumor Sequencing and Patient-Derived Xenografts in the Neoadjuvant Treatment of Breast Cancer

Background: Breast cancer patients with residual disease after neoadjuvant chemotherapy (NAC) have increased recurrence risk. Molecular characterization, knowledge of NAC response, and simultaneous generation of patient-derived xenografts (PDXs) may accelerate drug development. However, the feasibility of this approach is unknown. Methods: We conducted a prospective study of 140 breast cancer patients treated with NAC and performed tumor and germline sequencing and generated patient-derived xenografts (PDXs) using core needle biopsies. Chemotherapy response was assessed at surgery. Results: Recurrent “targetable” alterations were not enriched in patients without pathologic complete response (pCR); however, upregulation of steroid receptor signaling and lower pCR rates (16.7%, 1/6) were observed in triple-negative breast cancer (TNBC) patients with luminal androgen receptor (LAR) vs basal subtypes (60.0%, 21/35). Within TNBC, TP53 mutation frequency (75.6%, 31/41) did not differ comparing basal (74.3%, 26/35) and LAR (83.3%, 5/6); however, TP53 stop-gain mutations were more common in basal (22.9%, 8/35) vs LAR (0.0%, 0/6), which was confirmed in The Cancer Genome Atlas and British Columbia data sets. In luminal B tumors, Ki-67 responses were observed in tumors that harbored mutations conferring endocrine resistance (p53, AKT, and IKBKE). PDX take rate (27.4%, 31/113) varied according to tumor subtype, and in a patient with progression on NAC, sequencing data informed drug selection (olaparib) with in vivo antitumor activity observed in the primary and resistant (postchemotherapy) PDXs. Conclusions: In this study, we demonstrate the feasibility of tumor sequencing and PDX generation in the NAC setting. “Targetable” alterations were not enriched in chemotherapy-resistant tumors; however, prioritization of drug testing based on sequence data may accelerate drug development.

Performance characteristics of dedicated molecular breast imaging systems at low doses.

PURPOSE The purpose of this study was to compare the system performance characteristics and lesion detection capability of two molecular breast imaging (MBI) systems: a multicrystal sodium iodide (NaI)-based single-head system and a cadmium zinc telluride (CZT)-based dual-head system at low administered doses (150-300 MBq) of Tc-99m sestamibi. METHODS System performance characteristics including count sensitivity, uniformity, energy resolution, and spatial resolution were measured using standard NEMA methods, or a modified version thereof in cases where the standard NEMA protocol could not be applied. A contrast-detail phantom with 48 lesions at varying depths from the collimator surface was used to assess lesion contrast-to-noise-ratio (CNR) using background count densities comparable to those observed in patient studies performed with administered doses of 150 MBq Tc-99m sestamibi. Lesions with CNR >3 were deemed to be detectable. Thirty patients undergoing MBI examinations with administered doses of 150-300 MBq were scanned for an additional view on the pixelated NaI system. CNR was calculated for lesions observed on patient images. Background count densities of patient images were measured and compared between the two systems. RESULTS Over the central field of view, integral and differential uniformity were 6.1% and 4.2%, respectively, for the pixelated NaI system, and 3.8% and 2.7%, respectively, for the CZT system. Count sensitivity was 10.8 kcts/min/MBq for the NaI system and 32.9 kcts/min/MBq for the CZT system. Energy resolution was 13.5% on the pixelated NaI system and 4.5% on the CZT system. Spatial resolution (full-width at half-maximum) for the pixelated NaI detector was 4.2 mm at a distance of 1.2 cm from the collimator and 5.2 mm at 3.1 cm. Spatial resolution of a single CZT detector was 2.9 mm at a distance of 1.2 cm from the collimator and 4.7 mm at 3.1 cm. Effective spatial resolution obtained with dual-head CZT was below 4.7 mm throughout a simulated breast thickness of 6 cm. From contrast-detail phantom images of lesions at distances of 1.5-4.5 cm from the collimator face, the CZT system detected 124 of 144 (86%) of lesions compared to 97 of 144 (67%) with the NaI system. In patient studies, from comparison of the same view with both systems, a total of 7 breast lesions were identified on CZT system in seven patients, and 4 of 7 (57%) were detected on NaI system. Patient image background count densities on the CZT system were on average 3.4 times higher than those on the NaI system. CONCLUSIONS The CZT system demonstrated better uniformity, count sensitivity, spatial resolution, energy resolution, and lesion detection in phantom and patient studies compared to the NaI system. At administered doses of 150-300 MBq Tc-99m sestamibi, patient results obtained with CZT systems may not be directly translatable to NaI systems.

Comparison of Tc-99m maraciclatide and Tc-99m sestamibi molecular breast imaging in patients with suspected breast cancer

BackgroundMolecular breast imaging (MBI) performed with 99mTc sestamibi has been shown to be a valuable technique for the detection of breast cancer. Alternative radiotracers such as 99mTc maraciclatide may offer improved uptake in breast lesions. The purpose of this study was to compare relative performance of 99mTc sestamibi and 99mTc maraciclatide in patients with suspected breast cancer, using a high-resolution dedicated gamma camera for MBI. Women with breast lesions suspicious for malignancy were recruited to undergo two MBI examinations—one with 99mTc sestamibi and one with 99mTc maraciclatide. A radiologist interpreted MBI studies in a randomized, blinded fashion to assign an assessment score (1–5) and measured lesion size. Lesion-to-background (L/B) ratio was measured with region-of-interest analysis.ResultsAmong 39 analyzable patients, 21 malignant tumors were identified in 21 patients. Eighteen of 21 tumors (86%) were seen on 99mTc sestamibi MBI and 19 of 21 (90%) were seen on 99mTc maraciclatide MBI (p = 1). Tumor extent measured with both radiopharmaceuticals correlated strongly with pathologic size (99mTc sestamibi, r = 0.84; 99mTc maraciclatide, r = 0.81). The L/B ratio in detected breast cancers was similar for the two radiopharmaceuticals: 1.55 ± 0.36 (mean ± S.D.) for 99mTc sestamibi and 1.62 ± 0.37 (mean ± S.D.) for 99mTc maraciclatide (p = 0.53). No correlation was found between the L/B ratio and molecular subtype for 99mTc sestamibi (rs = 0.12, p = 0.63) or 99mTc maraciclatide (rs = −0.12, p = 0.64). Of 20 benign lesions, 10 (50%) were seen on 99mTc sestamibi and 9 of 20 (45%) were seen on 99mTc maraciclatide images (p = 0.1). The average L/B ratio for benign lesions was 1.34 ±0.40 (mean ±S.D.) for 99mTc sestamibi and 1.41 ±0.52 (mean ±S.D.) for 99mTc maraciclatide (p = 0.75). Overall diagnostic performance was similar for both radiopharmaceuticals. AUC from ROC analysis was 0.83 for 99mTc sestamibi and 0.87 for 99mTc maraciclatide (p = 0.64).Conclusions99mTc maraciclatide offered comparable lesion uptake to 99mTc sestamibi, in both malignant and benign lesions. There was good correlation between lesion extent and uptake measured from both radiopharmaceuticals. 99mTc maraciclatide offered a marginal (but not significant) improvement in sensitivity over 99mTc sestamibi. Our findings did not support an association between the uptake of either radiopharmaceutical and tumor molecular subtype.Trial registrationClinicalTrials.gov, NCT00888589

Establishing and characterizing patient-derived xenografts using pre-chemotherapy percutaneous biopsy and post-chemotherapy surgical samples from a prospective neoadjuvant breast cancer study

BackgroundPatient-derived xenografts (PDXs) are increasingly used in cancer research as a tool to inform cancer biology and drug response. Most available breast cancer PDXs have been generated in the metastatic setting. However, in the setting of operable breast cancer, PDX models both sensitive and resistant to chemotherapy are needed for drug development and prospective data are lacking regarding the clinical and molecular characteristics associated with PDX take rate in this setting.MethodsThe Breast Cancer Genome Guided Therapy Study (BEAUTY) is a prospective neoadjuvant chemotherapy (NAC) trial of stage I-III breast cancer patients treated with neoadjuvant weekly taxane+/-trastuzumab followed by anthracycline-based chemotherapy. Using percutaneous tumor biopsies (PTB), we established and characterized PDXs from both primary (untreated) and residual (treated) tumors. Tumor take rate was defined as percent of patients with the development of at least one stably transplantable (passed at least for four generations) xenograft that was pathologically confirmed as breast cancer.ResultsBaseline PTB samples from 113 women were implanted with an overall take rate of 27.4% (31/113). By clinical subtype, the take rate was 51.3% (20/39) in triple negative (TN) breast cancer, 26.5% (9/34) in HER2+, 5.0% (2/40) in luminal B and 0% (0/3) in luminal A. The take rate for those with pCR did not differ from those with residual disease in TN (p = 0.999) and HER2+ (p = 0.2401) tumors. The xenografts from 28 of these 31 patients were such that at least one of the xenografts generated had the same molecular subtype as the patient. Among the 35 patients with residual tumor after NAC adequate for implantation, the take rate was 17.1%. PDX response to paclitaxel mirrored the patients’ clinical response in all eight PDX tested.ConclusionsThe generation of PDX models both sensitive and resistant to standard NAC is feasible and these models exhibit similar biological and drug response characteristics as the patients’ primary tumors. Taken together, these models may be useful for biomarker discovery and future drug development.

Technical Note: Development of a combined molecular breast imaging/ultrasound system for diagnostic evaluation of MBI‐detected lesions

Purpose: The purpose of this study was to perform a pilot evaluation of an integrated molecular breast imaging/ultrasound (MBI/US) system designed to enable, in real‐time, the registration of US to MBI and diagnostic evaluation of breast lesions detected on MBI. Methods: The MBI/US system was constructed by modifying an existing dual‐head cadmium zinc telluride (CZT)‐based MBI gamma camera. The upper MBI detector head was replaced with a mesh panel, which allowed an ultrasound probe to access the breast. An optical tracking system was used to monitor the location of the ultrasound transducer, referenced to the MBI detector. The lesion depth at which ultrasound was targeted was estimated from analysis of previously acquired dual‐head MBI datasets. A software tool was developed to project the US field of view onto the current MBI image. Correlation of lesion location between both modalities with real‐time MBI/US scanning was confirmed in a breast phantom model and assessed in 12 patients with a breast lesion detected on MBI. Results: Combined MBI/US scanning allowed for registration of lesions detected on US and MBI as validated in phantom experiments. In patient studies, successful registration was achieved in 8 of 12 (67%) patients, with complete registration achieved in seven and partial registration achieved in one patient. In 4 of 12 (37%) patients, lesion registration was not achieved, partially attributed to uncertainty in lesion depth estimates from MBI. Conclusion: The MBI/US system enabled successful registration of US to MBI in over half of patients studied in this pilot evaluation. Future studies are needed to determine if real‐time, registered US imaging of MBI‐detected lesions may obviate the need to proceed to more expensive procedures such as contrast‐enhanced breast MRI for diagnostic workup or biopsy of MBI findings.

Adherence to Guidelines for Breast Surveillance in Breast Cancer Survivors

Background: Guidelines recommend annual mammography after curative-intent treatment for breast cancer. The goal of this study was to assess contemporary patterns of breast imaging after breast cancer treatment. Methods: Administrative claims data were used to identify privately insured and Medicare Advantage beneficiaries with nonmetastatic breast cancer who had residual breast tissue (not bilateral mastectomy) after breast surgery between January 2005 and May 2015. We calculated the proportion of patients who had a mammogram, MRI, both, or neither during each of 5 subsequent 13-month periods. Multinomial logistic regression was used to assess associations between patient characteristics, healthcare use, and breast imaging in the first and fifth years after surgery. Results: A total of 27,212 patients were followed for a median of 2.9 years (interquartile range, 1.8-4.6) after definitive breast cancer surgery. In year 1, 78% were screened using mammography alone, 1% using MRI alone, and 8% using both tests; 13% did not undergo either. By year 5, the proportion of the remaining cohort (n=4,790) who had no breast imaging was 19%. Older age was associated with an increased likelihood of mammography and a decreased likelihood of MRI during the first and fifth years. Black race, mastectomy, chemotherapy, and no MRI at baseline were all associated with a decreased likelihood of both types of imaging. Conclusions: Even in an insured cohort, a substantial proportion of breast cancer survivors do not undergo annual surveillance breast imaging, particularly as time passes. Understanding factors associated with imaging in cancer survivors may help improve adherence to survivorship care guidelines.

Best Practices in Molecular Breast Imaging: A Guide for Technologists

Molecular breast imaging (MBI) technologists must have a combination of both nuclear medicine skills and mammographic positioning skills. Currently, no formal programs offer this type of hybrid technologist training. The purpose of this perspective is to provide a best-practices guide for technologists performing MBI. Familiarity with best practices may aid in obtaining high-quality MBI examinations by decreasing the likelihood of image artifacts, positioning problems, and other factors that contribute to false-negative or false-positive findings.

Nodular fasciitis of the breast in an elderly woman

Nodular fasciitis is a benign proliferation of fibroblasts and myofibroblasts most commonly found in the soft tissues of the upper extremities and the trunk of young to middle-aged adults. Nodular fasciitis is infrequently encountered in the breast and in the elderly. We report a case of a 69-year-old woman presenting with a palpable breast mass with imaging features that mimicked malignancy. Knowledge of this entity is important to allow proper radiological and pathologic concordance and patient management.