Breast cancer, a heterogeneous disease, is now the most common cancer worldwide [12]. Many limitations have been identified in the currently available treatment modalities for breast carcinoma due to molecular evolution and tumor heterogeneity, changes in intrinsic subtypes during metastasis, and development of post-treatment complications [13, 14]. High IMP3 expression is a predictor of metastasis and poor survival [5, 15]. The role of IMP3 as an EMT promoter by binding to SLUG mRNA has been documented in literature [6].

Majority of the studies in literature have reported IMP3 positivity in breast carcinoma ranging from 33 to 35.6% [16,17,18]. Contrary to this, in the present study, IMP3 immunopositivity was seen in 86.7% of the breast carcinoma cases. This could be explained by geographical and demographic differences.

We found that IMP3 positivity was significantly higher in tumors of greater size (p < 0.05) and higher TNM stage (p < 0.05). IMP3 staining intensity also showed significant association with tumor histological grade (p = 0.009) and TNM stage (p = 0.036). Sjekloča et al. also reported a significant association between IMP3 positivity and tumor size and TNM stage [18]. Similar to our study results, Walter et al. also found a significantly higher expression of IMP3 in higher grade breast tumors (p < 0.001) [16]. In cancers other than breast cancer as well, a higher TNM stage is associated with IMP3 positivity [19, 20].

There are few studies in literature that have evaluated the IMP3 immunopositivity and staining intensity in different molecular subtypes of breast carcinoma. IMP3 expression in breast carcinoma has been mainly studied in triple negative breast cancer (TNBC). It has been reported that IMP3 promotes TNBC stem cell property [21, 22]. In the present study, the highest IMP3 positivity was seen in the luminal subtype followed by the TNBC subtype. However, this association was not statistically significant. IMP3 staining intensity, however, showed significant association with molecular subtype (p < 0.05) with the highest staining intensity seen in Her-2/neu-enriched subtype followed by TNBC. This could be explained by geographical and demographic differences in molecular subtyping of breast carcinoma and the smaller population of TNBC cases in our study.

No significant association was found between IMP3 positivity or staining intensity and other clinicopathological parameters like tumor laterality, menopausal status, in situ component, lymphovascular invasion, lymph node status, and ER/PR and HER-2/neu status. However, Walter et al. found significant association between IMP3 expression and ER, PR, and Her-2/neu-negative status, which could probably be explained by the entirely TNBC nature of their study population [16]. Sufficient information regarding the association of the rest of these clinicopathological characteristics with IMP3 is unavailable in current literature.

Previous studies on breast carcinoma have reported SLUG immunopositivity ranging from 34 to 100% [23,24,25]. In the present study, we found SLUG to be positive in 90% breast cancer cases, which is in line with the previous study results [24, 26].

SLUG positivity was significantly higher (p < 0.01) in TNM stage III. SLUG staining intensity was also found to have significant association with TNM stage (p < 0.01). This is in concordance with the findings of other studies [24, 26] but contrary to study results of Gu et al. as they found greater number of stage I and II cases to be SLUG positive [23].

SLUG positivity was found to be non-significantly higher in patients with lymph node involvement. However, Fouad et al. and Côme et al. reported a significant correlation between lymph node status and SLUG positivity [24, 27]. In contrast, Gu et al. found that higher SLUG expression is found in lymph node-negative cases [23]. This discordance in findings can be explained by the variation in population demographics.

We found SLUG positivity to be highest in luminal subtype, followed by TNBC subtype and least in Her-2/neu-enriched cases. Similar findings were reported by Fouad et al., while Gu et al. showed a statistically significant strong correlation between TNBC subtype and SLUG positivity [23, 24]. Thus, more studies with larger sample size are required to establish the relationship between SLUG and molecular subtypes of breast cancer. Further, the small population of cancers of the TNBC subtype in our study could also account for this discrepancy.

No significant association was found between SLUG positivity or staining intensity and other factors like menopausal status, tumor laterality, size, grade, in situ component, lymphovascular invasion, ER/PR and HER-2 status, and molecular subtype. Fouad et al., however, found that SLUG expression was higher in ER- and PR-negative cases [24]. This difference could be possibly due to differences in population characteristics. Sufficient information regarding the association of the rest of these clinicopathological characteristics with SLUG is not available in current literature.

We found a highly significant association (p < 0.001) between IMP3 and SLUG immunopositivity with 86.67% cases showing positivity for both. All IMP3-positive cases were found to be SLUG positive. IMP3 induces EMT by binding SLUG mRNA, which may explain the association found between the two proteins. However, out of 54 SLUG-positive cases, 2 were IMP3 negative, thus implicating a minor pathway of SLUG expression that is unrelated to IMP3. SLUG is also known to be regulated by other proteins such as TGF-β and GSK-3β, which may further explain this [28]. IMP3 and SLUG staining intensities also showed highly significant correlation (p < 0.001). These findings are in accordance with studies conducted by Su et al. and Samanta et al. where they studied the relationship between IMP3 and SLUG in breast carcinoma via mRNA-based studies [29, 30]. Samanta et al. discovered that IMP3 binds avidly to SLUG mRNA, hence, regulating its expression by binding to the 5′ UTR. SLUG, in turn, targets SOX2, which is a stem cell factor. Thus, establishing a mechanism of breast tumor initiation involving IMP3 and providing a basis for its association with aggressiveness and poor outcome of breast carcinoma [30]. Su et al. found that IMP3 expression directly correlated with both SLUG (p = 0.004) and vimentin (p < 0.001) suggesting that SLUG acts as a functional target of IMP3. In the present study, our findings are also in accordance with these.

In our study, however, there was a lack of follow-up for disease recurrence and progression after modified radical mastectomy due to the outbreak of the COVID-19 pandemic. Hence, disease-free survival and overall survival could not be calculated. Further, our study was retrospective and also had a small cohort due to constraints of time, resources, and the pandemic.