Novel PET tracers in breast cancer for treatment optimization: clinical utility and future perspectives.

PURPOSE OF REVIEW: There is a critical need for timely and accurate decisions in breast cancer management. This narrative review aims to clarify the potential role of novel PET tracers in optimizing treatment strategies for different breast cancer subtypes. RECENT FINDINGS: 2-deoxy-2-[18F]-fluoro-D-glucose PET/computed tomography (FDG PET/CT) has a pivotal role in response assessment in metastatic breast cancer, despite its limitations in certain histological and molecular subtypes. Further PET radiopharmaceuticals have been proposed to address these clinical needing. SUMMARY: FES PET/CT demonstrates its usefulness in assessing ER expression and predicting response to therapy in luminal breast cancer, with implications for treatment optimization and monitoring. In HER2-positive and HER2-low breast cancer, HER2-targeted PET tracers show potential in assessing HER2 status, while their accuracy in predicting response to targeted therapies is still debated. PARP-targeted PET imaging holds potential for selecting patients for PARP inhibitors treatments, particularly in triple-negative breast cancer (TNBC), where imaging tools are crucial due to the absence of specific targets. Immunotherapy and antibody-drug conjugates (ADCs) are emerging treatment options for TNBC, and PET imaging targeting immune checkpoints could aid in treatment selection and response monitoring. The dynamic role of PET/CT imaging in tailoring breast cancer treatments requires further multidisciplinary research to validate the clinical utility of targeted tracers.

Diagnostic performance of image-guided vacuum-assisted breast biopsy after neoadjuvant therapy for breast cancer: prospective pilot study.

BACKGROUND: Image-guided vacuum-assisted breast biopsy (VABB) of the tumour bed, performed after neoadjuvant therapy, is increasingly being used to assess residual cancer and to potentially identify to identify pathological complete response (pCR). In this study, the accuracy of preoperative VABB specimens was assessed and compared with surgical specimens in patients with triple-negative or human epidermal growth factor receptor 2 (HER2)-positive invasive ductal breast cancer after neoadjuvant therapy. As a secondary endpoint, the performance of contrast-enhanced MRI of the breast and PET-CT for response prediction was assessed. METHODS: This single-institution prospective pilot study enrolled patients from April 2018 to April 2021 with a complete response on imaging (iCR) who subsequently underwent VABB before surgery. Those with a pCR at VABB were included in the primary analysis of the accuracy of VABB. The performance of imaging (MRI and PET-CT) was analysed for prediction of a pCR considering both patients with an iCR and those with residual disease at postneoadjuvant therapy imaging. RESULTS: Twenty patients were included in the primary analysis. The median age was 44 (range 35-51) years. At surgery, 18 of 20 patients showed a complete response (accuracy 90 (95 per cent exact c.i. 68 to 99) per cent). Only two patients showed residual ductal intraepithelial neoplasia of grade 2 and 3 respectively. In the secondary analysis, accuracy was similar for MRI and PET-CT (77 versus 78 per cent; P = 0.76). CONCLUSION: VABB in patients with an iCR might be a promising method to select patients for de-escalation of surgical treatment in triple-negative or HER2-positive breast cancer. The present results support such an approach and should inform the design of future trials on de-escalation of surgery.

Imaging for illuminating actionable pathways in breast cancer.

PURPOSE OF REVIEW: Nuclear medicine has the potential to explore and illuminate several pathways in breast cancer (BC) offering different radiopharmaceuticals for positron emission tomography (PET) designed to target specific tumor characteristics. The aim of this critical review is to give an overview about emerging opportunities in PET imaging, underlining the future potential contribution in the management of BC patients. RECENT FINDINGS: Beside 2-deoxy-2-[ 18 F]-fluoro- d -glucose (FDG), new generation tracers for PET imaging have been recently proposed to investigate specific characteristics in breast cancer, both targeting tumor cells and the tumor micro-environment (TME). SUMMARY: FDG-PET is a procedure that received extensive clinical validation. However, its role in BC is still suboptimal due to the low-FDG avidity of specific tumor subtypes. Human epidermal growth receptor-2 and integrin targeted PET radiotracers might provide useful information selecting patients more likely to respond to target therapy. FluoroEstradiol (FES) is a FDA-approved PET radiotracer targeting the estrogen receptor (ER), useful to investigate metastatic ER+ patients, to assess in vivo ER heterogeneity and to evaluate hormonal therapy efficacy. Inhibitors of the fibroblast activation protein (FAPi) targeting the cancer-associated fibroblast can explore the TME with PET imaging. FAPi is also proposed a theranostic agent for radio-ligand therapy.

How to Perform Repeat Sentinel Node Biopsy Safely After a Previous Mastectomy: Technical Features and Oncologic Outcomes.

BACKGROUND: The latest National Comprehensive Cancer Network Breast Cancer Guidelines still discourage repeat sentinel node biopsy (SNB) after mastectomy, and the largest multicentric study available reports only 35 cases in the absence of previous axillary dissection (AD). METHODS: From January 2003 to November 2018, 89 patients of the European Institute of Oncology with local recurrence of breast cancer after mastectomy, free of distant metastases, with a clinically negative axilla and a negative axillary ultrasound, in absence of AD, underwent lymphatic mapping before wide local excision. RESULTS: During surgery, SNB was successful for 99% of the patients, with 14% being metastatic. Additional metastatic nodes removed by AD after a positive sentinel node occurred in 82% of cases. After a medium follow-up period of 3.7 years, the overall survival rate was 96.7%, and the disease-free survival rate was 84.4%. No axillary relapse after AD was recorded. One patient who refused human epidermal growth factor receptor 2 (HER2)-targeted treatment experienced ipsilateral axillary recurrence after a negative repeat SNB. The first axillary level was never directly irradiated because all the patients with positive repeat SNB underwent AD. For invasive luminal-like HER2-negative recurrences, the metastatic sentinel node was significantly associated with the choice to prescribe adjuvant chemotherapy (p = 0.003). CONCLUSIONS: In specialized centers, repeat axillary SNB for patients with local recurrence after mastectomy in the absence of previous AD can represent a safe option for detection and removal of occult axillary disease that would otherwise not be excised/irradiated to achieve better local control and could possibly influence the choice of adjuvant treatments.

Does failed mapping predict sentinel lymph node metastasis in cN0 breast cancer?

Aims: The clinical significance of nonvisualized sentinel lymph nodes (non-vSLNs) is unknown. The authors sought to determine the incidence of non-vSLNs on lymphoscintigraphy, the identification rate during surgery, factors associated with non-vSLNs and related axillary management. Patients & methods: A total of 30,508 consecutive SLN procedures performed at a single institution from 2000 to 2017 were retrospectively studied. Associations between clinicopathological factors and the identification of SLNs during surgery were assessed. Results: Non-vSLN occurred in 525 of the procedures (1.7%). In 73.3%, at least one SLN was identified intraoperatively. Nodal involvement was only significantly associated with SLN nonidentification (p < 0.001). Conclusion: Patients with non-vSLN had an increased risk for SLN metastasis. The detection rate during surgery was consistent, reducing the amount of unnecessary axillary dissection.

Lay abstract To study the clinical significance of nonvisualized sentinel lymph nodes (non-vSLNs) in axillary surgery for breast cancer, 30,508 consecutive SLN procedures performed at a single institution from 2000 to 2017 were retrospectively reviewed with the aim to analyze the incidence of non-vSLNs on lymphoscintigraphy, the identification rate during surgery, factors associated with non-vSLNs and related axillary management. Associations between clinicopathological factors and the identification of SLNs during surgery were assessed. Non-vSLN occurred in 525 of the procedures (1.7%). In 73.3%, at least one SLN was identified intraoperatively. Nodal involvement was only significantly associated with SLN nonidentification (p < 0.001). Patients with non-vSLN had an increased risk for SLN metastasis. The detection rate during surgery was consistent, reducing the amount of unnecessary axillary dissection.

How Useful Are Tumor Markers in Detecting Metastases with FDG-PET/CT during Breast Cancer Surveillance?

BACKGROUND: To assess the clinical usefulness of serum tumor markers for early detection of distant breast cancer recurrence using FDG-PET/CT. METHODS: We retrospectively analyzed 561 consecutive patients who underwent surgery for invasive primary breast cancer and had increased tumor markers (CA 15-3 and CEA) after completion of locoregional therapy. FDG-PET/CT data were reviewed for all cases. CA 15-3 and CEA were evaluated both in a continuous and in a quartile (Q) distribution. The Wilcoxon rank-sum test and logistic regression models were used to evaluate the association between increased tumor marker values and the presence (and type) of distant metastases. RESULTS: The median value of CA 15-3 was 35.0 U/mL (IQR, 29.5-43.0) in cases where no distant metastases were detected, and it was 58.9 U/mL (IQR, 40.0-108.0) in cases where metastases were detected (p < 0.001). The median value of CEA was 6.6 U/mL (IQR, 4.4-10.0) in cases of no metastases and 12.4 U/mL (IQR, 6.9-30.0) in cases of metastases (p < 0.001). Increased levels of both tumor markers (Q3 and Q4) were strongly associated with the presence of distant metastases. The association between CA 15-3 and bone/liver metastases was stronger compared with other types of metastases (p heterogeneity between odds ratios [ORs] = 0.03 for Q3 and <0.001 for Q4), while no relevant heterogeneity between ORs emerged for CEA. CONCLUSION: Increased tumor marker levels detected in asymptomatic breast cancer patients during adjuvant therapies and follow-up are significantly predictive of distant metastases identified on FDG-PET/CT.

Multicentric breast cancer with heterogeneous histopathology: a multidisciplinary review.

Multiple synchronous (multifocal or multicentric) ipsilateral breast cancers with heterogeneous histopathology are a rare clinical occurrence, however, their incidence is increasing due to the use of MRI for breast cancer screening and staging. Some studies have demonstrated poorer clinical outcomes for this pattern of breast cancer, but there is no evidence to guide clinical practice. In this multidisciplinary review, we reflect on pathology and molecular characteristics, imaging findings, surgical management including conservation and reconstructive options and approach to the axilla, and the role of chemotherapy and radiotherapy. Multidisciplinary discussions appear decisive in planning an appropriate surgical choice and defining the correct systemic treatment tailored to each clinical condition.

Role of interim 18F-FDG-PET/CT for the early prediction of clinical outcomes of Non-Small Cell Lung Cancer (NSCLC) during radiotherapy or chemo-radiotherapy. A systematic review.

BACKGROUND: Non-Small Cell Lung Cancer (NSCLC) is characterized by aggressiveness and includes the majority of thorax malignancies. The possibility of early stratification of patients as responsive and non-responsive to radiotherapy with a non-invasive method is extremely appealing. The distribution of the Fluorodeoxyglucose (18F-FDG) in tumours, provided by Positron-Emission-Tomography (PET) images, has been proved to be useful to assess the initial staging of the disease, recurrence, and response to chemotherapy and chemo-radiotherapy (CRT). OBJECTIVES: In the last years, particular efforts have been focused on the possibility of using ad interim 18F-FDG PET (FDGint) to evaluate response already in the course of radiotherapy. However, controversial findings have been reported for various malignancies, although several results would support the use of FDGint for individual therapeutic decisions, at least in some pathologies. The objective of the present review is to assemble comprehensively the literature concerning NSCLC, to evaluate where and whether FDGint may offer predictive potential. METHODS: Several searches were completed on Medline and the Embase database, combining different keywords. Original papers published in the English language from 2005 to 2016 with studies involving FDGint in patients affected by NSCLC and treated with radiation therapy or chemo-radiotherapy only were chosen. RESULTS: Twenty-one studies out of 970 in Pubmed and 1256 in Embase were selected, reporting on 627 patients. CONCLUSION: Certainly, the lack of univocal PET parameters was identified as a major drawback, while standardization would be required for best practice. In any case, all these papers denoted FDGint as promising and a challenging examination for early assessment of outcomes during CRT, sustaining its predictivity in lung cancer.

Long-term results of PRRT in advanced bronchopulmonary carcinoid.

PURPOSE: Peptide receptor radionuclide therapy (PRRT) for the treatment of neuroendocrine tumours (NET) has been explored for almost two decades, but there are still few trials that have exclusively investigated well-differentiated and moderately differentiated NET arising from the respiratory tree. Thus, the aim of this study was to explore the outcome in patients affected by bronchopulmonary carcinoid (BPC) following PRRT. METHODS: We retrospectively analysed 114 patients with advanced stage BPC consecutively treated with PRRT at the European Institute of Oncology, Milan, from 1997 to 2012 and followed until October 2014. The objective responses, overall survival (OS) and progression-free survival (PFS) were rated, and three different PRRT protocols ((90)Y-DOTATOC vs. (177)Lu-DOTATATE vs. (90)Y-DOTATOC + (177)Lu-DOTATATE) were compared with regard to their efficacy and tolerability. RESULTS: The median OS (evaluated in 94 of the 114 patients) was 58.8 months. The median PFS was 28.0 months. The (177)Lu-DOTATATE protocol resulted in the highest 5-year OS (61.4%). Morphological responses (partial responses + minor responses) were obtained in 26.5% of the cohort and were associated with longer OS and PFS. The (90)Y-DOTATOC + (177)Lu-DOTATATE protocol provided the highest response rate (38.1%). Adverse events were mild in the majority of patients. However, haematological toxicity negatively affected survival. No severe (grade 3/4) serum creatinine increase was observed. Patients treated with (90)Y-DOTATOC alone more frequently showed a mild/moderate decrease in renal function. In patients treated with chemotherapy before PRRT had a shorter OS and PFS, and a higher risk of developing nephrotoxicity. CONCLUSION: In a large cohort of patients with advanced BPC treated in a "real-world" scenario and followed up for a median of 45.1 months (range 2-191 months), PRRT proved to be promising in prolonging survival and delaying disease progression. Despite the potential selection biases, considering the risk-benefit ratio, (177)Lu-DOTATATE monotherapy seems the best option for PRRT. Our results indicate that the use of PRRT in earlier stages of the disease could provide a more favorable outcome.

A PET-Surrogate Signature for the Interrogation of the Metabolic Status of Breast Cancers.

Metabolic alterations in cancers can be exploited for diagnostic, prognostic, and therapeutic purposes. This is exemplified by 18F-fluorodeoxyglucose (FDG)-positron emission tomography (FDG-PET), an imaging tool that relies on enhanced glucose uptake by tumors for diagnosis and staging. By performing transcriptomic analysis of breast cancer (BC) samples from patients stratified by FDG-PET, a 54-gene signature (PETsign) is identified that recapitulates FDG uptake. PETsign is independently prognostic of clinical outcome in luminal BCs, the most common and heterogeneous BC molecular subtype, which requires improved stratification criteria to guide therapeutic decision-making. The prognostic power of PETsign is stable across independent BC cohorts and disease stages including the earliest BC stage, arguing that PETsign is an ab initio metabolic signature. Transcriptomic and metabolomic analysis of BC cells reveals that PETsign predicts enhanced glycolytic dependence and reduced reliance on fatty acid oxidation. Moreover, coamplification of PETsign genes occurs frequently in BC arguing for their causal role in pathogenesis. CXCL8 and EGFR signaling pathways feature strongly in PETsign, and their activation in BC cells causes a shift toward a glycolytic phenotype. Thus, PETsign serves as a molecular surrogate for FDG-PET that could inform clinical management strategies for BC patients.

Role of 18FDG PET/CT in patients treated with 177Lu-DOTATATE for advanced differentiated neuroendocrine tumours.

PURPOSE: The prognostic value of FDG PET for neuroendocrine tumours (NETs) has been reported. In this study we evaluated the role of FDG PET in predicting response and progression-free survival (PFS) after (177)Lu-DOTATATE peptide receptor radionuclide therapy (Lu-PRRT) in patients with advanced well-differentiated grade 1/2 NETs. METHODS: We retrospectively evaluated 52 patients with progressive advanced NETs overexpressing somatostatin receptors and treated with Lu-PRRT with a cumulative activity up to 27.7 GBq divided into five courses. According to WHO 2010/ENETS classification, patients were stratified into two groups: those with grade 1 tumour (Ki-67 index ≤2 %, 19 patients), and those with grade 2 tumour (Ki-67 index >3 % to <20 %, 33 patients). On the basis of the FDG PET scan, 33 patients were classified as PET-positive (PET+) and 19 as PET-negative (PET-). RESULTS: FDG PET was positive in 57 % of patients with grade 1 NET and in 66 % of patients with grade 2 NET, and the rates of disease control (DC, i.e. complete response + partial response + stable disease) in grade 1 and grade 2 patients were 95 % and 79 %, respectively (P = 0.232). In PET- and PET+ patients, the DC rates were 100 % and 76 % (P = 0.020) with a PFS of 32 and 20 months, respectively (P = 0.033). Of the PET+ patients with grade 1 NET, 91 % showed disease control, whereas about one in three PET+ patients with grade 2 NET (32 %) progressed after Lu-PRRT (DC rate 68 %). CONCLUSION: These results suggest that FDG PET evaluation is useful for predicting response to Lu-PRRT in patients with grade 1/2 advanced NETs. Notably, none of PET- patients had progressed at the first follow-up examination after Lu-PRRT. Grade 2 NET and PET+ (arbitrary SUV cutoff >2.5) were frequently associated with more aggressive disease. PET+ patients with grade 2 NET, 32 % of whom did not respond to Lu-PRRT monotherapy, might benefit from more intensive therapy protocols, such as the combination of chemotherapy and PRRT.

FDG and Non-FDG Radiopharmaceuticals for PET Imaging in Invasive Lobular Breast Carcinoma.

Invasive lobular cancer (ILC) is the second most frequent histological type of breast cancer (BC) and includes a heterogeneous spectrum of diseases with unique characteristics, especially the infiltrative growth pattern and metastatic spread. [18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (FDG-PET/CT) is extensively used in oncology and BC patient evaluation. Its role in ILCs is considered suboptimal due to its low FDG avidity. Therefore, ILCs could benefit from molecular imaging with non-FDG tracers that target other specific pathways, contributing to precision medicine. This narrative review aims to summarize the current literature on the use of FDG-PET/CT in ILC and to discuss future opportunities given by the development of innovative non-FDG radiotracers.

Imaging Cancer-Associated Fibroblasts (CAFs) with FAPi PET.

The tumor microenvironment (TME) surrounding tumor cells is a complex and highly dynamic system that promotes tumorigenesis. Cancer-associated fibroblasts (CAFs) are key elements in TME playing a pivotal role in cancer cells' proliferation and metastatic spreading. Considering the high expression of the fibroblast activation protein (FAP) on the cell membrane, CAFs emerged as appealing TME targets, namely for molecular imaging, leading to a pan-tumoral approach. Therefore, FAP inhibitors (FAPis) have recently been developed for PET imaging and radioligand therapy, exploring the clinical application in different tumor sub-types. The present review aimed to describe recent developments regarding radiolabeled FAP inhibitors and evaluate the possible translation of this pan-tumoral approach in clinical practice. At present, the application of FAPi-PET has been explored mainly in single-center studies, generally performed in small and heterogeneous cohorts of oncological patients. However, preliminary results were promising, in particular in low FDG-avid tumors, such as primary liver and gastro-entero-pancreatic cancer, or in regions with an unfavorable tumor-to-background ratio at FDG-PET/CT (i.e., brain), and in radiotherapy planning of head and neck tumors. Further promising results have been obtained in the detection of peritoneal carcinomatosis, especially in ovarian and gastric cancer. Data regarding the theranostics approach are still limited at present, and definitive conclusions about its efficacy cannot be drawn at present. Nevertheless, the use of FAPi-based radio-ligand to treat the TME has been evaluated in first-in-human studies and appears feasible. Although the pan-tumoral approach in molecular imaging showed promising results, its real impact in day-to-day clinical practice has yet to be confirmed, and multi-center prospective studies powered for efficacy are needed.

Investigation of 18F-FDG PET in the selection of patients with breast cancer as candidates for sentinel node biopsy after neoadjuvant therapy.

PURPOSE: The main objective of this study was to determine the role of [(18)F]-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) in the selection of patients with breast cancer as candidates for sentinel node biopsy (SNB) after neoadjuvant therapy. METHODS: Forty-four patients with primary breast cancer clinically classified as cT2, cT3 or cT4(a-c) cN0-N2 or cN3 M0 and with a baseline FDG PET scan positive both in the site of primary tumour and axillary lymph nodes underwent neoadjuvant therapy and then a second FDG PET scan. In the case of axillary FDG PET uptake, patients underwent axillary lymph node dissection (ALND). If the second FDG PET scan was negative for axillary involvement, SNB was performed in order to evaluate axillary lymph node status. Only in the case of SN positivity did total ALND follow. RESULTS: Specificity and positive predictive value of FDG PET for detection of axillary lymph node metastases after neoadjuvant therapy were as high as 83% (95% confidence interval: 51-97%) and 85% (95% confidence interval: 54-97%), respectively, whereas sensitivity, negative predictive value and diagnostic accuracy were inadequate for a correct staging (34, 32 and 48%, respectively). CONCLUSION: The poor sensitivity of FDG PET in detecting axillary lymph node metastases makes SNB mandatory in cases of a negative scan. The relatively high positive predictive value seems to suggest a role of FDG PET in selecting patients who, after neoadjuvant therapy, are candidates for ALND, avoiding SNB. However, this issue requires confirmation in a larger series of patients.

18F-FDG PET/CT in asymptomatic patients with COVID-19: the submerged iceberg surfaces.

OBJECTIVE: The aim of this case series is to describe our experience in diagnosis and management of oncological asymptomatic patients with COVID-19 who underwent 18F-FDG PET/CT. METHODS: From March 9 to March 31, 2020, we identified 5 patients who had PET/CT findings suspicious for COVID-19, but no symptom of infection. RESULTS: The first three patients were administered an SARS-CoV-2 test in a COVID-dedicated center, while the fourth and fifth were tested in our institution, in accordance with a new internal procedure. The SARS-CoV-2 test yielded positive results in all five patients. CONCLUSION: In this COVID-19 emergency, our task as radiologists and nuclear medicine physicians is to be able to identify imaging findings suggestive of the disease and to manage patients without overloading the hospital system.