PET/CT and breast cancer subtypes

Imaging Molecular Targets and Metabolic Pathways in Breast Cancer for Improved Clinical Management: Current Practice and Future Perspectives

Breast cancer is the most frequently diagnosed cancer and leading cause of cancer-related deaths worldwide. Timely decision-making that enables implementation of the most appropriate therapy or therapies is essential for achieving the best clinical outcomes in breast cancer. While clinicopathologic characteristics and immunohistochemistry have traditionally been used in decision-making, these clinical and laboratory parameters may be difficult to ascertain or be equivocal due to tumor heterogeneity. Tumor heterogeneity is described as a phenomenon characterized by spatial or temporal phenotypic variations in tumor characteristics. Spatial variations occur within tumor lesions or between lesions at a single time point while temporal variations are seen as tumor lesions evolve with time. Due to limitations associated with immunohistochemistry (which requires invasive biopsies), whole-body molecular imaging tools such as standard-of-care [18F]FDG and [18F]FES PET/CT are indispensable in addressing this conundrum. Despite their proven utility, these standard-of-care imaging methods are often unable to image a myriad of other molecular pathways associated with breast cancer. This has stimulated interest in the development of novel radiopharmaceuticals targeting other molecular pathways and processes. In this review, we discuss validated and potential roles of these standard-of-care and novel molecular approaches. These approaches' relationships with patient clinicopathologic and immunohistochemical characteristics as well as their influence on patient management will be discussed in greater detail. This paper will also introduce and discuss the potential utility of novel PARP inhibitor-based radiopharmaceuticals as non-invasive biomarkers of PARP expression/upregulation.

Combined 18F-FDG and 18F-Alfatide II PET May Predict Luminal B (HER2 Negative) Subtype and Nonluminal Subtype of Invasive Breast Cancer

Noninvasive PET molecular imaging using radiopharmaceuticals is important to classify breast cancer in the clinic. The aim of this study was to investigate the combination of ¹⁸F-FDG and ¹⁸F-Alfatide II for predicting molecular subtypes of invasive breast cancer. Forty-four female patients with clinically suspected breast cancer were recruited and underwent ¹⁸F-FDG and ¹⁸F-Alfatide II PET/CT within a week. Tracer uptake in breast lesions was assessed using the maximum standardized uptake value (SUV_max), mean standardized uptake value (SUV_mean), and SUV_max ratio of ¹⁸F-FDG to ¹⁸F-Alfatide II (FAR). Invasive breast cancer lesions were further classified as luminal A subtype, luminal B subtype, human epidermal growth factor receptor-2 (HER2) overexpressing subtype, and triple negative subtype according to the expression of the estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki-67. Among 44 patients, 35 patients were pathologically diagnosed with invasive breast cancer. The SUV_max and SUV_mean of ¹⁸F-FDG were significantly higher in the ER-negative group than those in the ER-positive group, as well as in the PR-negative group than those in the PR-positive group. However, the SUV_max and SUV_mean of ¹⁸F-Alfatide II were higher in the ER-positive group and the PR-positive group. By combining ¹⁸F-FDG and ¹⁸F-Alfatide II, the FAR was lower in the ER-positive group and the PR-positive group. The HER2 overexpressing subtype showed the highest SUV_max and SUV_mean for ¹⁸F-FDG while the luminal B (HER2 negative) subtype revealed the lowest values. The luminal B (HER2 negative) subtype showed the highest ¹⁸F-Alfatide II SUV_max, while the triple negative subtype showed the lowest ¹⁸F-Alfatide II SUV_max. The FAR was the lowest in the luminal B (HER2 negative) subtype and much higher in the HER2 overexpressing and triple negative subtypes. FAR less than 1 predicted the luminal B (HER2 negative) subtype with high specificity (93.1%) and NPV (90%). FAR greater than 3 predicted the HER2 overexpressing subtype and triple negative subtype (namely, the nonluminal subtype) with very high specificity (100%) and PPV (100%). In summary, FAR, the combined PET parameter of ¹⁸F-FDG and ¹⁸F-Alfatide II, can be used to predict molecular subtypes of invasive breast cancer, especially for the luminal B (HER2 negative) subtype and the nonluminal subtype.

Perspectives on the Systemic Staging in Newly Diagnosed Breast Cancer

Breast cancer is a complex disease, and accurate systemic staging is an essential aspect of the evaluation of a patient with newly diagnosed breast cancer. Considering that the chance of having metastatic disease at breast cancer diagnosis is different in each patient and depends on a variety of anatomic and biologic factors, it is crucial to understand that some populations may benefit from more intensive staging because their pretest probability of metastatic disease is higher than that of the average patient. Identifying these patients with de novo stage IV breast cancer is associated with substantial prognostic and therapeutic implications. Unfortunately, recent advances in understanding breast cancer heterogeneity and molecular biology have not been incorporated in the international guidelines and recommendations about imaging examinations for detecting de novo metastatic breast cancer. This review article discusses important issues regarding the rationale for performing systemic staging, addresses current and innovative imaging methods, and proposes an algorithm for systemic staging in patients with newly diagnosed breast cancer.

The Evolving Role of FDG-PET/CT in the Diagnosis, Staging, and Treatment of Breast Cancer

The applications of 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography/X-ray computed tomography (PET/CT) in the management of patients with breast cancer have been extensively studied. According to these studies, PET/CT is not routinely performed for the diagnosis of primary breast cancer, although PET/CT in specific subtypes of breast cancer correlates with histopathologic features of the primary tumor. PET/CT can detect metastases to mediastinal, axial, and internal mammary nodes, but it cannot replace the sentinel node biopsy. In detection of distant metastases, this imaging tool may have a better accuracy in detecting lytic bone metastases compared to bone scintigraphy. Thus, PET/CT is recommended when advanced-stage disease is suspected, and conventional modalities are inconclusive. Also, PET/CT has a high sensitivity and specificity to detect loco-regional recurrence and is recommended in asymptomatic patients with rising tumor markers. Numerous studies support the future role of PET/CT in prediction of response to neoadjuvant chemotherapy (NAC). PET/CT has a higher diagnostic value for prognostic risk stratification in comparison with conventional modalities. With the continuing research on the treatment planning and evaluation of patients with breast cancer, the role of PET/CT can be further extended.

Breast-specific gamma imaging with Tc-99m-sestamibi in the diagnosis of breast cancer and its semiquantitative index correlation with tumor biologic markers, subtypes, and clinicopathologic characteristics

OBJECTIVES

To determine the sensitivity of breast-specific gamma imaging (BSGI) in diagnosing breast cancer and assess the potential correlation between the semiquantitative index of BSGI and biologic markers, molecular subtypes, and clinicopathologic characteristics of breast cancer.

MATERIALS AND METHODS

The sensitivity of BSGI for breast cancer was retrospectively assessed in 102 female breast cancer patients who underwent BSGI before surgery and was compared with that of ultrasonography and mammography. BSGI was visually graded on the basis of the Society of Nuclear Medicine and Molecular Imaging guideline. Tracer uptake in the cancer as the lesion to nonlesion ratio (L/N) was calculated semiquantitatively and was subsequently correlated to tumor biologic markers, molecular subtypes, and clinicopathologic characteristics.

RESULTS

The sensitivity of BSGI for breast cancer by visual analysis was 94.1% (96/102) in our cohort, which was 100% (47/47) in the subgroup of patients with a tumor size more than 2.0 cm and 89.1% (49/55) in the subgroup of patients with a size less than or equal to 2.0 cm. The sensitivity of BSGI was significantly higher than that of ultrasonography of 84.2% (85/101) (P=0.022) and mammography of 84.5% (60/71) (P=0.037). There was no significant correlation between the L/N and expressions of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, and antigen Ki-67, and the subtypes or histologic grade of the cancer (P>0.05). However, the value of L/N was associated with infiltration degree (P=0.005), axillary lymph node status (P=0.029), and tumor size (P=0.002). Multivariate analysis further indicated that the value of L/N was correlated with infiltration degree (P=0.016) and tumor size (P=0.002).

CONCLUSION

BSGI has a high sensitivity for detecting primary breast cancer. The value of L/N on BSGI was independently related to infiltration degree and tumor size of breast cancer, but not to expression of tumor receptor markers and histologic grade.