[18F]Fluoroestradiol-PET/CT Imaging of Invasive Lobular Carcinoma

According to the National Comprehensive Cancer Network (NCCN) 2018 guidelines 18F-2-fluoro-2-deoxy-D-glucose (FDG)-PET/CT may be performed as an alternative to a contrast-enhanced CT of the chest, abdomen and pelvis and Tc-99m methylene diphosphonate (MDP) bone scan for evaluation of distant metastatic disease in newly diagnosed stage III breast cancer patients. FDG-PET/CT is usually not obtained for stage I or stage II breast cancer patients as change in patient management is rare. Prior studies have demonstrated FDG-PET/CT can identify sites of unsuspected metastatic disease in newly diagnosed breast cancer patients thereby altering treatment decisions given that palliative management is typical for stage IV disease, whereas neoadjuvant therapy followed by surgery and postoperative radiation may be considered for stage II and operable stage III disease. These guidelines consider invasive breast cancer as a single entity and do not consider whether tailoring imaging techniques for subtypes of breast cancer may be beneficial. However, prior research suggests that FDG-PET/CT may be more appropriate as an alternative to CT and bone scan for patients with invasive ductal carcinoma (IDC) rather than invasive lobular carcinoma (ILC) as FDG demonstrates comparatively reduced sensitivity for ILC metastases. Compared to IDC, ILC is more often occult on mammography, ultrasound, and FDG-PET/CT; which is of importance for clinical management as ILC is more often multifocal and bilateral compared to IDC. Clinical breast examination also has lower sensitivity for detection of ILC compared to IDC, even for large tumors, as ILC may be indistinguishable from normal breast tissue on palpation. A prior study evaluating systemic staging of newly diagnosed patients with stage I-III invasive breast cancer found that FDG-PET/CT is 1.98 times less likely to reveal unsuspected distant metastatic disease for women with ILC compared to IDC. In this study, all IDC metastases demonstrated FDG avidity whereas 25% of ILC metastases (3 of 12) were not FDG avid. Detection of local axillary metastatic disease on FDG-PET/CT was also lower for ILC (0 of 146 patients) compared to IDC (7 of 89 patients) despite data from the Surveillance, Epidemiology and End Results (SEER) database demonstrating similar rates for lymph node metastases between IDC and ILC. Another study evaluating FDG-PET/CT for the diagnosis of primary breast cancer found that the false negative rate for detection of ILC by FDG was 65% (15 of 23 cases) compared to 23% for IDC (23 of 97 cases) when matching for tumors of the same size. A final study reported a false negative rate of FDG for ILC detection of 13% (2 of 15 patients). Mechanistically, ILC may not take up FDG as avidly as IDC due to lower tumor microvascularity, cellular density, proliferation rate, and number of glucose transporters (GLUT). ILC osseous metastatic disease is also more frequently occult on FDG-PET/CT compared to IDC as ILC osseous metastases are more frequently sclerotic, whereas FDG-PET/CT is more sensitive for lytic osseous metastases. Sclerotic ILC osseous metastases also may be indistinguishable from benign bone islands on CT at initial staging, thereby necessitating biopsy or imaging follow-up for confirmation of osseous metastatic disease. Improved imaging strategies for primary and metastatic ILC are therefore warranted. Multiple studies have proven the efficacy of FES-PET/CT for imaging evaluation of ER+ invasive breast malignancy (evaluating both IDC and ILC together, with the large majority of cases comprising IDC) but, to our knowledge, no prior study has focused FES-PET/CT evaluation only to cases of ILC, nor have prior studies compared FES-PET/CT directly with FDG-PET/CT for evaluation of newly diagnosed ILC. Given that all prior studies on FES-PET/CT have grouped a small number of ILC cases with a larger number of IDC cases, the imaging performance of FES-PET/CT specifically for ILC is unknown. ILC demonstrates higher rates of ER positivity than IDC with prior studies showing greater than 90% positivity for cases of ILC. Data from the SEER database also shows ILC demonstrates higher overall expression of ER than IDC (ILC 95% positive for ER, n=17,503 vs IDC 74% positive for ER, n=172,379). FES-PET/CT may therefore be suitable for imaging evaluation of a high proportion of patients with ILC.

One session of [18F]FES PET/CT Imaging - COMPLETED Up to three imaging sessions: [18F] FES-PET/CT exam, Optional [18F]FDG PET/CT scan and Optional follow-up [18F] FES-PET/CT exam.

Hypothesize that FES-PET/CT will detect at least 80% of histologically proven primary ILC estrogen receptor positive (ER+) tumors.

This outcome evaluates whether cancer staging will change when assessed via FES-PET/CT compared to assessment based on standard of care imaging (Yes/No). Null hypothesis is that the proportion of patients with a change in staging is 5% or less. The alternative hypothesis is that the proportion of patients with a change in staging is 20% or more.

Rate of estrogen receptor positive (ER+) ILC that does not demonstrate positive FES uptake - COMPLETED AS OF MARCH 2022

FES-PET/CT concordance with ER status from biopsy and presence of inter-tumoral ER heterogeneity. Focal uptake above background with standardized update value (SUV)-max of 1.5 or greater

Rate of estrogen receptor negative (ER-) ILC that does demonstrate positive FES uptake - COMPLETED AS OF MARCH 2022

FES-PET/CT concordance with ER status from biopsy and presence of inter-tumoral ER heterogeneity. Focal uptake above background with SUV max of 1.5 or greater

FES-PET/CT concordance with ER status from biopsy and presence of inter-tumoral ER heterogeneity. Focal uptake above background with SUV max of 1.5 or greater. Presence of FES uptake with SUV max of 1.5 or greater in some but not all biopsy proven or suspected metastatic lesions

Evaluate the rate of discordant uptake (FES positive/FDG negative or FES negative/FDG positive) - COMPLETED AS OF MARCH 2022

Differences between FDG- and FES PET/CT uptake. Discordant uptake will be evaluated for biopsy proven primary, any proven or suspected local nodal (axillary, intramammary, internal mammary, supraclavicular) and any proven or suspected distant metastatic lesions.

Assess whether quantity of methylated ctDNA at baseline (primary study arm, n=40) predicts patient stage at presentation

Spearman correlation will be used to assess the correlation between circulating tumor DNA (ctDNA) and stage.

A proportional hazards model will be used to assess the relationship between methylated ctDNA and overall survival. To determine the relationship at various time points, the analysis will be performed with censoring at 6, 12, 18, 24, 36, 48 and 60 months.

Assess relationship between presence of heterogeneous FES-PET/CT update at baseline and overall survival

Kaplan-Meier methods and a log rank test will be used to assess the relationship between FES-PET/CT and overall survival.

FOR PILOT PHASE COMPLETED IN 2021: Inclusion Criteria: Adults aged 18 years or greater All patients or legal guardians are willing and able to sign a written informed consent and HIPAA authorization in accordance with local and institutional guidelines. Histologically confirmed invasive lobular carcinoma within the past 12 weeks confirmed from biopsy of primary tumor or metastasis. Patient is willing to have their clinical records reviewed for at least 24 months after enrollment. FOR PILOT PHASE COMPLETED IN 2021: Exclusion Criteria: Patients with known allergic or hypersensitivity reactions to previously administered radiopharmaceuticals. Patients with significant drug or other allergies or autoimmune diseases may be enrolled at the Investigator's discretion. Patients who require monitored anesthesia for PET/CT scanning. Patients who are too claustrophobic to undergo PET/CT scanning. Pregnancy or current breast feeding. Any patient that is medically unstable defined as patient requiring inpatient hospitalization or needing evaluation at an acute care or urgent care facility at time of imaging. Patients undergoing treatment with estrogen receptor agonists (such as fulvestrant and tamoxifen) within 5 weeks of the FES-PET/CT scan. (Note that aromatase inhibitors and luteinizing hormone-releasing hormone agonists do not affect ER expression, or binding of FES to ER, and do not need to be discontinued or considered for inclusion or exclusion of patients). Patient who have had the site(s) of biopsy proven invasive lobular carcinoma surgically resected. FOR EXPANSION PHASE ADDED IN MARCH 2022 AMENDMENT: INCLUSION CRITERIA: Adults aged 18 years or greater All patients or legal guardians are willing and able to sign a written informed consent and HIPAA authorization in accordance with local and institutional guidelines. Patient must qualify for one of the following: Primary endpoint analysis/Primary Arm: Histologically confirmed ER+ invasive lobular carcinoma within the past 16 weeks confirmed from biopsy of primary tumor or metastasis (n=40). Exploratory Arm 1: Histologically confirmed ER+ invasive lobular carcinoma at any time in the past, confirmed from biopsy of primary tumor or metastasis, with confirmed or imaging suspected metastatic disease, currently on antihormonal therapy or chemotherapy (n=10). Exploratory Arm 2: Histologically confirmed ER- invasive lobular carcinoma (at any point) at any site with biopsy-proven or imaging suspected metastatic ILC (n=5). Patient is willing to have their clinical records reviewed, and be contacted by phone during follow-up intervals specified, for approximately 60 months after enrollment. Patient is willing to provide baseline blood specimens for ctDNA analysis. FOR EXPANSION PHASE ADDED IN MARCH 2022 AMENDMENT: EXCLUSION CRITERIA: Patients with known allergic or hypersensitivity reactions to previously administered radiopharmaceuticals. Patients with significant drug or other allergies or autoimmune diseases may be enrolled at the Investigator's discretion. Patients who require monitored anesthesia for PET/CT scanning. Patients who are too claustrophobic to undergo PET/CT scanning. Pregnancy or current breast feeding. Patient who have had the site(s) of biopsy proven invasive lobular carcinoma surgically resected. Note: This does not apply for participants being enrolled for Exploratory Arm 1. Patients undergoing treatment with estrogen receptor agonists (such as fulvestrant and tamoxifen) within 5 weeks of the FES-PET/CT scan. (Note that aromatase inhibitors and luteinizing hormone-releasing hormone agonists do not affect ER expression, or binding of FES to ER, and do not need to be discontinued or considered for inclusion or exclusion of patients). Note: This does not apply for participants being enrolled for Exploratory Arm 1.