The reported pooled sensitivity for FDG-PET/CT is 71% to 88% and specificity is 69% to 79.3% [117,120,132,133]. Most of the studies do not specifically report on response of the regional lymph nodes. In one meta-analysis of four studies involving 920 patients, the sensitivity of FDG-PET/CT for regional lymph node response assessment is 92% [118]. In another meta-analysis of 987 abstracts, only four were eligible for analysis, yielding a PPV between 40% and 100% [134]. The timing of FDG-PET/CT is critical and varies between studies, with some investigators demonstrating FDG- PET/CT has more accuracy during NAC (after first or second cycles of chemotherapy) than after NAC, whereas MRI performed better at the end of NAC [118,133]. MRI had higher sensitivity in predicting the pathologic response after NAC in 13 studies involving 575 patients, and FDG-PET/CT had a higher specificity in these same 13 studies involving 618 patients [132]. Currently, there is lack of consensus that early response detected by imaging tests translates into improved overall outcomes. A negative FDG-PET/CT during or after NAC does not necessarily correlate with final pathological node-negative disease, as demonstrated in one series of 206 patients [119]. SUV values may underestimate or overestimate response when the residual tumor is small. Some investigators have reported SUVmax <2.5 as negative [120], whereas others demonstrated that the change in SUV before and after NAC or change between the pre-NAC FDG-PET/CT examination and the examination performed after the first or second cycle of NAC were better predictors of response [134-136]. Despite the research, there is no accurate noninvasive test to replace SLNB or ALND at this time. However, one benefit of using FDG-PET/CT is that this examination can also evaluate other sites of metastases in a single study [102]. A search for a noninvasive restaging technique for identifying patients with axillary complete response is ongoing.
Imaging of the Axilla. The reported pooled sensitivity for FDG-PET/CT is 71% to 88% and specificity is 69% to 79.3% [117,120,132,133]. Most of the studies do not specifically report on response of the regional lymph nodes. In one meta-analysis of four studies involving 920 patients, the sensitivity of FDG-PET/CT for regional lymph node response assessment is 92% [118]. In another meta-analysis of 987 abstracts, only four were eligible for analysis, yielding a PPV between 40% and 100% [134]. The timing of FDG-PET/CT is critical and varies between studies, with some investigators demonstrating FDG- PET/CT has more accuracy during NAC (after first or second cycles of chemotherapy) than after NAC, whereas MRI performed better at the end of NAC [118,133]. MRI had higher sensitivity in predicting the pathologic response after NAC in 13 studies involving 575 patients, and FDG-PET/CT had a higher specificity in these same 13 studies involving 618 patients [132]. Currently, there is lack of consensus that early response detected by imaging tests translates into improved overall outcomes. A negative FDG-PET/CT during or after NAC does not necessarily correlate with final pathological node-negative disease, as demonstrated in one series of 206 patients [119]. SUV values may underestimate or overestimate response when the residual tumor is small. Some investigators have reported SUVmax <2.5 as negative [120], whereas others demonstrated that the change in SUV before and after NAC or change between the pre-NAC FDG-PET/CT examination and the examination performed after the first or second cycle of NAC were better predictors of response [134-136]. Despite the research, there is no accurate noninvasive test to replace SLNB or ALND at this time. However, one benefit of using FDG-PET/CT is that this examination can also evaluate other sites of metastases in a single study [102]. A search for a noninvasive restaging technique for identifying patients with axillary complete response is ongoing.