Neoadjuvant chemotherapy plays an increasingly prominent role in the management of locally advanced breast cancer. For large tumors at initial presentation, neoadjuvant therapy is indicated to decrease tumor size and increase the breast conservation rate. Patients who want to undergo breast conserving surgery (BCS) but are not candidates at diagnosis can benefit from neoadjuvant therapy with BCS rates as high as 72.3%. There are many other instances when neoadjuvant therapy may be considered, for example, patients with chemoresponsive breast cancers like human epidermal growth factor receptor (HER) 2–positive breast cancer and triple-negative breast cancer (TNBC). If a patient presents with nodal involvement, then initiating the multidisciplinary care with chemotherapy has become commonplace with pathologic complete response rates approaching 40%. Breast PET imaging (BPI) can facilitate the management of patients undergoing neoadjuvant chemotherapy for large tumor size, chemoresponsive subtypes and/or nodal involvement.
Breast PET imaging (BPI) requires the intravenous injection of a small amount of fluorine-18 fluorodeoxyglucose followed by a one hour wait for the metabolically active cancer cells to uptake the tracer. Tomographic scans are then performed with the patient seated and the breasts gently compressed between two detectors. Positioning is analogous to mammography providing easy image correlation. BPI technology demonstrates an intrinsic spatial resolution of 1.6 mm. High sensitivity and specificity have been documented for this breast imaging tool, 92.5% and 91.2% respectively.
Axillary views can also be obtained and initial clinical studies have shown high specificity, and PPV, but a lower sensitivity, 99%, 92% and 46% respectively. Several factors affect lesion detectability in BPI imaging of the axilla, primarily lesion to background activity, background noise level, and lesion location.
When used for initial evaluation of the newly diagnosed breast cancer patient, BPI may identify tumors larger than previously seen with the standard imaging of mammography and ultrasound or as noted on physical exam. This could convert some patients to appropriately receive neoadjuvant care prior to surgical intervention. With initiation of neoadjuvant chemotherapy (NAC, chemotherapy before surgery), repeat PET imaging can monitor the response to treatment. Definitive data is not currently available, but some sites have investigated the use of a repeat scan after the first therapy to evaluate the response with potential alteration of chemotherapy treatment and to predict potential complete response rates. More commonly, a scan is repeated after therapy is complete, prior to surgery, to confirm the ability to undergo a breast conservation procedure. Pilot clinical data using BPI to characterize tumor size in largest dimension and lesion maximum uptake value (PUV max) pre and post NAC correlated with final surgical pathology has shown great promise with 90.69% sensitivity and 94.73% specificity.
Classically, an axillary node dissection has been performed for patients with a clinically positive axilla identified prior to NAC. It has become increasingly accepted that sentinel node biopsy may be performed for those patients if a complete clinical response to chemotherapy can be documented and an adequate number of nodes can be retrieved at the time of the sentinel procedure. Breast PET imaging of the axilla is limited in its ability to routinely see nodal disease less than 6 mm, but it is highly accurate for larger lesions and can be readily used to monitor therapy. The specificity and positive predictive value are superior to other imaging tools.
Further studies are necessary to confirm the role of breast PET imaging in patients receiving neoadjuvant chemotherapy. Early work shows a role in managing the timing of surgery and chemotherapy, evaluating the axilla, and possibly modifying chemotherapy treatments based on tumor response to chemotherapy.
Case Study: Pathologic Complete Response (pCR); Multifocal IDC after chemotherapy
BPI before chemotherapy:
BPI no residual uptake after chemotherapy:
BPI=Breast PET Imaging
Largest dimension 4.5 cm; PUVMAX 6.2
Images Courtesy Dr. Jane Nelson, Austin Cancer Center, Austin, TX