Role of MRI is well established in locoregional staging of breast cancer, response assessment to neoadjuvant therapy and screening in high-risk patients. A standard MRI protocol involves both the T2w and DWI sequences along with pre- and post-contrast fat saturated T1w images with dynamic contrast study [12]. It is important to develop non-invasive imaging markers of prognosis to personalize and guide therapy. Till date, various imaging features have been found to correlate with pathological factors and are based on the lesion morphology, enhancement characteristics and diffusion coefficients.
T2w STIR images have been used to increase the specificity of MRI. Lesions can be differentiated as benign or malignant based on their T2w signal intensity as breast cancers are known to have low signals owing to their increased cellularity and low water content, few exceptions being mucinous & metaplastic variants of invasive ductal carcinomas [13]. Also, presence of edema around the lesion favors malignancy [14].
Underlying reason for PE has been attributed to various underlying mechanisms. An important reason postulated is the neo-angiogenesis associated with malignant process. These vessels are leaky and thus lead to exudation of fluid [15]. Second reason is the altered microenvironment of the surrounding peritumoral tissue. It has been found that the levels of polysaccharide hyaluronan are increased that leads to increased T2 relaxation times [15, 16]. Another basis for the PE is the lymphovascular invasion. Presence of LVI portends a poor prognosis as this implies that the tumor cells have already seeded the lymphovascular space and thus the likelihood of positive nodal disease and the disease recurrence [17, 18].
We did not find a statistically significant correlation between the PE and LVI and this may be attributed to the fact that other factors also play role in causing PE. These results match those by Mori et al. and are supported by Uematsu et al. who reported that it is pre-pectoral edema that is found to be more commonly associated with LVI rather than the PE [3, 19]. Cheon et al. also found no statistically significant results [20]. However, in another study done by the same authors where they evaluated MRI imaging features to predict LVI in node negative patients after appropriately matched controls and the exclusion of in situ disease associated malignancies, they found statistically significant correlation between the presence of LVI and the edema [17]. The difference may be in that we did not exclude the in situ component from our study that might also cause increased perilesional signals on T2w images [21].
Recently, PE on T2w images has been found to be a useful finding that can act as an important prognostic factor in breast cancer. PE has been included in the imaging lexicon by The Cancer Genome Atlas research study group in breast cancer [22].
The prognostic significance of PE on T2w STIR images in patients of breast cancer has been evaluated by few recent studies.
In our study, we found that there existed no correlation between PE and the histological tumor type. These results are similar to those of Cheon et al. and Panizironi et al. [20, 23]. Out of the total five cases of invasive lobular cancers, PE was found in only one case (Fig. 3). Low propensity of invasive lobular cancers to have edema is probably due to their growth pattern as single sheets of cells along the normal tissue planes [18, 24]. We need more numbers of lobular carcinoma in the study group to obtain statistical significance.
We found that edema was more often associated with non-luminal tumors especially the triple negative subtype, while luminal A cancers were rarely associated with PE as found by other authors in their studies [20, 23, 25] (Fig. 3). This is explained by the fact that triple negative cancers are high-grade tumors with high proliferation index. Bae et al. in their study on response to neoadjuvant therapy in triple negative tumors found that the presence of PE was associated with worse distant metastasis-free survival [7].
We found that tumors with PE tend to be of higher grade with a high Ki-67 index. In our study, 62.5% of the tumors with peritumoral edema on MRI were grade 3 in line with studies by Cheon et al. (56%) and Panizorini et al. (63%) [20, 23]. They also found that these tumors were of high proliferation index as by Song et al. [20, 23, 26].
Although no statistical significant correlation existed between the PE and the pN stage, it was found that these patients tend to have higher nodal stage as opposed to those without edema. These results are similar to those obtained in previous studies [20].
