Axillary surgery in breast cancer (BC) is no longer a therapeutic procedure but has become a purely staging procedure. The progressive improvement in imaging techniques has paved the way to the hypothesis that prognostic information on nodal status deriving from surgery could be obtained with an accurate diagnostic exam. Positron emission tomography/magnetic resonance imaging (PET/MRI) is a relatively new imaging tool and its role in breast cancer patients is still under investigation.
Modern diagnostic imaging tools provide an accurate local and systemic staging in order to plan the primary treatment and to tailor the best surgical procedure. Whilst mammography, ultrasound (US) and magnetic resonance imaging (MRI) represent an excellent option to stage the T, staging the axilla with imaging is still challenging. To date, several studies have demonstrated the limitations of axillary ultrasound (Ax-US); these include the fact that it is an operator-dependent technique, its sensitivity ranges from 23% to 80% and also, it is unable to estimate the true axillary tumor burden [1][2][5,6]. Similarly, other tools such as standard breast MRI [3][7], Positron Emission Mammography (PEM) [4][8], PET/CT [5][9] are not accurate enough to predict axillary stage. On the one hand, two large meta-analyses have shown that Ax-US and selective needle biopsy correctly identifies around 50–55% of node-positive patients [2][6][6,10]. On the other hand, when considering the tumor burden, having abnormal nodes on Ax-US, mammogram and MRI often equates to having only 1–2 positive sentinel nodes that do not always change surgical plans [3][7][8][7,11,12]. However, the accuracy is not excellent and even when Ax-US identifies fewer than two abnormal nodes, patients are still more likely to have more than three positive nodes [9][13].
PET/MRI is a relatively new imaging tool, and its field of application is still being studied. It was introduced in 2011 in the USA and UE, offering the potential to combine the specificity obtained by the functional imaging of PET with the superior sensitivity of MRI, and provide relevant information of higher diagnostic accuracy [19][23]. In particular, the fully integrated PET/MRI system provides a simultaneous imaging acquisition [20][24].
As regards BC, the application of PET/MRI was studied in four different settings: for preoperative staging at diagnosis, for follow-up staging, to predict the prognosis and the response to therapy (Table 1).
Category Group | Reference | Total Number of Patients Nr. BC/tot. pts. (%) |
Study Design | Patient Position | Type of Acquisition |
---|---|---|---|---|---|
STAGING | Catalano, O.A., 2013 [21][25] Huellner, M.W., 2014 [22][26] Drzezga, A., 2012 [23][27] Appenzeller, P., 2013 [24][28] Wiesmuller, M., 2013 [25][29] Kirchner, J., 2018 [26][30] Botsikas, D., 2019 [27][32] Pace, L., 2014 [28][36] Kong, E., 2014 [29][33] Melsaether, A.N., 2016 [30][39] Van Nijnatten, T.J., 2018 [31][44] Taneja, S., 2014 [32][41] Grueneisen, J., 2015 [33][42] Botsikas, D., 2016 [34][40] Catalano, O.A., 2017 [35][37] Goorts B., 2017 [36][45] Kirchner, J., 2020 [37][34] Bruckmann, N.M., 2020 [38][35] Bruckmann, N.M., 2021 [39][38] |
35/134 (26.1%) 5/106 (4.8%) 3/32 (9.4%) 7/63 (11.1%) 3/46 (6.5%) 38/38 (100%) 80/80 (100%) 36/36 (100%) 42/42 (100%) 51/51 (100%) 12/12 (100%) 36/36 (100%) 49/49 (100%) 58/58 (100%) 51/51 (100%) 40/40 (100%) 56/56 (100%) 104/104 (100%) 154/154 (100%) |
retrospective prospective prospective prospective prospective prospective prospective prospective prospective prospective prospective retrospective prospective retrospective retrospective prospective prospective prospective prospective |
supine supine supine supine supine supine WB, prone B supine WB, prone B supine supine WB, prone B supine prone supine WB, prone B prone supine WB, prone B NA prone supine WB, prone B supine WB, prone B supine |
simultaneous sequential simultaneous sequential simultaneous simultaneous sequential simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous sequential simultaneous simultaneous simultaneous simultaneous simultaneous |
FOLLOW-UP | Grueneisen, J., 2017 [40][31] Sawicki, L.M., 2016 [41][46] Pujara, A.C., 2016 [42][47] Beiderwellen, K., 2013 [43][48] Chandarana, H., 2013 [44][49] Rauscher, I., 2014 [45][50] Catalano, O.A., 2015 [46][51] Raad, R.A., 2016 [47][52] Ishii S., 2016 [48][53] Kirchner, J., 2017 [49][54] Sonni, I., 2019 [50][55] |
36/36 (100%) 21/21 (100%) 35/35 (100%) 10/70 (14%) 10/32 (31.2%) 4/40 (10%) 109/109 (100%) 15/208 (7.2%) 33/123 (26.8%) 2/41 (5%) 23/74 (31%) |
prospective prospective retrospective prospective prospective prospective retrospective retrospective prospective prospective prospective |
supine NA prone NA NA NA NA NA NA NA NA |
simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous |
PROGNOSIS | Schiano, C., 2020 [51][56] Margolis, N.E., 2016 [52][57] Catalano, O.A., 2017 [53][58] Jena, A., 2017 [54][59] Jena, A., 2017 [55][60] Kong, E., 2018 [56][61] Incoronato, M., 2018 [57][62] Inglese, M., 2019 [58][63] Incoronato, M., 2019 [59][64] Morawitz, J., 2021 [60][65] Murakami, W., 2020 [61][66] Carmona-Bozo, J.C., 2021 [62][67] |
40/217 (18.4%) 12/12 (100%) 21/21 (100%) 69/69 (100%) 98//98 (100%) 46/46 (100%) 50/50 (100%) 46/46 (100%) 77/155(49.7%) 56/56 (100%) 55/55 (100%) 32/32 (100%) |
retrospective prospective retrospective prospective prospective prospective prospective prospective prospective prospective retrospective prospective |
NA prone supine WB, prone B supine WB, prone B prone prone prone prone supine WB, prone B prone supine WB, prone B prone |
simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous simultaneous |
RESPONSE | Jena, A., 2017 [63][68] Wang, J., 2017 [64][69] Romeo, V., 2017 [65][70] Cho, N., 2018 [66][71] Andreassen, M.M.S., 2020 [67][72] |
50/50 (100%) 14/14 (100%) 4/4 (100%) 26/26 (100%) 24/24 (100%) |
prospective prospective prospective prospective prospective |
supine WB, prone B prone NA supine WB, prone B NA |
simultaneous simultaneous simultaneous simultaneous simultaneous |
On the one hand, the advantages of this hybrid diagnostic tool are a lower radiation dose when compared to PET/CT, better inter-observer agreement, a one-stage exam and more accurate detection of brain, bone and liver metastases. On the other hand, PET/MRI is still an expensive and time-consuming imaging method, which is not available everywhere; despite the attractiveness of performing a single exam when both PET and MR imaging are indicated, PET/MRI also exhibits other limitations (i.e., long duration, MR truncation, PET/MRI misregistration, etc.) [68][43].
To conclude, the role of PET/MRI in the BC setting is not yet well defined, although it shows good accuracy in BC local and systemic staging and could be considered in both monitoring and predicting the response to PST. However, the heterogeneity of the studies reported and the variability of the PET/MRI approach limit the comparison and the summation of data. Hence, current evidence is not sufficient to derive standard indications; ongoing and future research on PET/MRI could help clarify its role and establish whether it may represent a useful diagnostic and prognostic tool, or if it needs to be replaced or integrated with other conventional diagnostic tools.
Several studies have investigated the power of PET/MRI in staging the axilla; the results are encouraging but preliminary, due to the small sample size and inhomogeneous study population and design (Table 2).
Authors | Total Number of Patients | Study Design | Patient Position | Type of Acquisition | Axillary Node Detection Sensitivity | Axillary Node Detection Specificity |
---|---|---|---|---|---|---|
Kirchner, J., 2018 [26][30] | 38 | prospective | supine WB, prone B | simultaneous | 93% | 95% |
Botsikas, D., 2019 [27][32] | 80 | prospective | supine WB, prone B | sequential | 0.85 (0.72–0.93) | 0.89 (0.82–0.94) |
Melsaether, A.N., 2016 [30][39] | 51 | prospective | supine | simultaneous | 88–100% (CI 69, 97) | 95% (CI 88, 98) |
Taneja, S., 2014 [32][41] | 36 | retrospective | supine WB, prone B | simultaneous | 60% on PET, 93.3% on MRI | 91% on PET and MRI |
Grueneisen, J., 2015 [33][42] | 49 | prospective | prone | simultaneous | 78% (CI 52, 94) | 90% (CI 74, 98) |
Botsikas, D., 2016 [34][40] | 58 | retrospective | supine WB, prone B | sequential | 79% | 100% |