Introduction
Ductal carcinoma
in situ (DCIS) of the breast refers to a premalignant lesion composed of malignant epithelial cells that have yet to invade through the basement membrane of the duct into the surrounding stroma [
1‐
3]. This heterogeneous group of neoplastic lesions, which is considered a precursor to invasive ductal carcinoma (IDC), accounts for approximately 20% of newly diagnosed breast cancer cases in the USA [
4] with incidence peaking in women aged 65–69 years. Clinically, DCIS is commonly detected through routine screening mammograms, and often presents as microcalcifications (approximately 80–90% of DCIS cases) [
5] and less often as a palpable mass (approximately 8% of cases) [
6,
7]. Advancements in screening mammography coupled with additional diagnostic mammography, ultrasound, and/or breast MRI for patients who present with a suspicious lesion are not only important for the characterization of ipsilateral disease [
8‐
10] but have also greatly increased the detection of DCIS lesions [
11]. As a result, significant increases in DCIS incidence have been observed across all ages but more predominantly in postmenopausal women [
12]. Indeed, data from the surveillance, epidemiology, and end results (SEER) program have shown that the incidence of DCIS increased approximately sevenfold between 1980 and 2001 [
11].
DCIS is considered a non-obligatory precursor of invasive breast carcinoma (IBC), where left untreated 14–64% of DCIS patients progress to invasive cancer within 10 years [
13‐
15]. It has been estimated that women with a history of DCIS have a 1.5–10-fold greater risk of subsequent IBC, and thus women diagnosed with DCIS have a threefold greater risk of dying from breast cancer than those without [
16,
17]. DCIS is stratified into three grades based on nuclear grade, i.e., corresponding to low (grade 1), intermediate (grade 2), and high grade (grade 3) [
18]. Although not all cases of DCIS will progress to invasive breast cancer it is thought that the grade of DCIS at the time of diagnosis is related to the likelihood of progression to IBC and the rapidity with which it is likely to occur [
19]. Several meta-analysis studies suggest that an increased risk of ipsilateral recurrence is associated with high-grade DCIS; however, a meta-analysis by Zhang et al. suggests that DCIS grade is not significantly associated with the risk of invasive recurrence [
20]. Inconsistencies in the ability to predict progression to invasive breast disease for those DCIS patients indicate that nuclear grade is not an ideal discriminant. The fact that among women with DCIS treated with surgical resection alone 20–40% of cases experience a recurrence in the same breast, with half of those women recurring with IBC [
21,
22] further highlights the need for identification of consistent and reproducible predictors of DCIS outcomes.
Currently, the majority of women diagnosed with DCIS are treated with breast-conserving surgery followed by radiation therapy (RT). Although, the addition of radiation therapy decreases local recurrence by about 50%, from 28.1 to 12.9%, the 15-year breast cancer-specific mortality rate from DCIS treated by lumpectomy alone without radiation therapy is only 2.33% [
23,
24]. Consequently, a majority of patients diagnosed with DCIS lesions undergo excessive treatments, and thus improved diagnostic tools are urgently needed to predict both the risk of local recurrence and/or DCIS progression to IBC. In addition to DCIS grade, several clinicopathological features of DCIS routinely assessed in all cases have emerged for their association with higher local recurrence rates and include absence of estrogen receptor, larger DCIS lesion size, positive margin status, and younger patient age [
25]. Additional immunohistochemical markers which are not routinely assessed during initial DCIS diagnosis have shown an association with progression to IBC and include expression of p16, COX2 and Ki67 and HER2 [
26].
In 2012, the Oncotype DX
® Breast DCIS test was developed for evaluation of DCIS lesions by RT-qPCR quantification of 12 of the 21 genes from the original Oncotype DX
® Breast cancer assay, utilized for recurrence risk stratification of primary breast tumors [
27]. This 12-gene assay is used to obtain a score based on the expression of 7 cancer-related genes (Ki67, AURKA/STK15, BIRC5/survivin, CCNB1, MYBL2, PGR, and GSTM1) and 5 normalizing reference genes (ACTB, GAPDH, RPLPO, GUS, and TFRC) [
27]. Expression analysis can be done on either whole tissue [
28‐
30], or archived formalin-fixed paraffin-embedded (FFPE) sections [
31‐
33]. Clinically tested, the Oncotype DX
® Breast DCIS assay has been used to predict the 10-year local recurrence risk of ipsilateral DCIS and/or IBC recurrence by stratifying patients into low (< 39), intermediate (39–54), and high (>= 55) risk score groups [
34]. When originally introduced in 2012, the recurrence risk was estimated solely based on the DCIS score; however, in 2018 it was refined to include patient age in local recurrence risk estimates; specifically, premenopausal patients were reported at higher local recurrence risk at all DCIS scores [
35,
36]. This molecular scoring system has been moderately used by clinicians to evaluate the risk of recurrence as well as for the evaluation of treatment strategies.
MicroRNAs (miRNA) are a class of endogenous short (22±2 nucleotides), noncoding RNAs that are known to be involved in virtually all cellular processes [
37]. MiRNAs are key posttranscriptional regulators of gene expression which generally exert their effects by binding directly to the 3’ untranslated region (UTR) of their target mRNA transcripts, destabilizing the mRNA, leading to translational silencing and ultimately the repression of protein production [
38‐
40]. Their expression regulation effects are intricate, as a single miRNA can regulate the expression of multiple genes [
41], and each mRNA may be regulated by multiple miRNAs [
42]. Tissue miRNA expression studies have examined their expression changes in relation to different physiological and pathological states [
43]. Indeed, the deregulation of miRNA expression has been shown to contribute to the development and progression of a variety of human malignancies, including breast cancer [
44], categorizing miRNAs in a novel class of oncogenes and/or tumor suppressor RNA molecules [
45].
Studies that we have performed using archived FFPE tissue specimens have demonstrated that optimized high-throughput gene expression technologies are suitable for the retrospective analysis of miRNAs [
46‐
49]. Our analyses with FFPE tissues as old as 35 years have shown reproducible detection of miRNAs highlighting their robust nature and molecular resilience to degradation and decay [
48]. Recently, our laboratory identified a subset of miRNAs, which displayed differential expression between DCIS lesions of patients who went on to develop invasive breast cancer, by comparison to DCIS lesions from control patients who did not develop breast cancer within the same time interval [
48].
In this study, we selected archived FFPE specimens from 41 women diagnosed with DCIS between 2012 and 2018, whose DCIS lesions were initially classified by the Oncotype DX® Breast DCIS score, and we evaluated the correlation between miRNA expression and DCIS scores. We used next-generation small-RNA sequencing to initially identify miRNA expression differences and then used RT quantitative PCR to validate our findings. As an additional measure, we evaluated miRNA expression changes based on the age of the patients diagnosed with DCIS.
Discussion
Advancements in modern high-quality screening and diagnostic mammography are widely acknowledged to have resulted in a significant increase in the detection and diagnosis of ductal carcinoma
in situ (DCIS) [
52]. The likelihood of DCIS recurrence or the progression to invasive breast cancer (IBC), however, is poorly understood, and for women diagnosed with DCIS, it remains difficult to predict who will go on to recur and/or to develop IBC [
53‐
55]. As such, the 12-gene DCIS Oncotype DX
® assay was developed and has been shown to allow for a more comprehensive molecular evaluation of DCIS lesions. This score-based assay, which stratifies patients into either low, intermediate, or high-risk groups, has been shown to successfully evaluate the risk of local recurrence and as such may help guide treatment strategies [
56]. Increasingly, more studies have shown that there is a direct relationship between the deregulation of miRNAs and the onset/progression of a variety of cancers [
57‐
59]. In this study we sought to determine the utility of correlating miRNA expression data from archived formalin-fixed paraffin-embedded (FFPE) specimens obtained from women diagnosed with DCIS, whose lesions were evaluated with the Oncotype DX
® DCIS assay and with known risk scores. For this retrospective study, we used methodologies we developed to analyze small RNAs, which we demonstrated to be applicable for the analysis of archived FFPE specimens up to 35 years old [
48].
Multiple studies have begun to evaluate miRNA expression changes in tumors as diagnostic and prognostic tools [
60‐
64]. Assessment of miRNA expression patterns has shown that they can act as oncogenes or tumor suppressors and display up- or downregulated expression patterns in many human tumors [
65]. It has been documented, for example, that DCIS tissue lesions exhibits a general upregulation in miR-21 expression when compared to normal breast tissue [
44,
66,
67]. It has been shown that the upregulation of miR-654 in DCIS lesions is associated with poor patient prognosis [
68]. Conversely, the expression of miR-125b has been shown to be downregulated in DCIS lesions [
69]. In normal breast tissue, the expression of miR-124, miR-145, and miR-205 appears enriched exclusively in the basal compartment of ducts, whereas in matching breast tumors their expression appears to be reduced [
70]. When comparing normal breast tissue to atypical ductal hyperplasia (ADH), DCIS lesions, and invasive ductal carcinoma (IDC), Chen et al identified that miR-21, miR-200b/c, miR-183, and miR-141 displayed an increase expression associated with histological progression toward invasive lesions [
66]. Altogether, these studies have highlighted the strong potential for using miRNA expression quantification as a means for molecular evaluation of DCIS lesions.
In the current study, we utilized risk scores obtained with the Oncotype DX
® DCIS assay as an initial classifier to perform miRNA next-generation sequencing (NGS) of classified DCIS lesions (i.e., high-, intermediate-, and low-risk scores). Our NGS analyses revealed a linear relationship between increased Oncotype DX
® DCIS risk scores and the deregulated expression of 15 miRNAs (either up- or downregulation). To further evaluate the robustness of our NGS findings, we quantified the expression of these 15 miRNAs by qRT-PCR using total RNA purified from archived DCIS lesions, classified with the Oncotype DX
® DCIS assay. These analyses revealed a strong correlation between expression downregulation of miR-30c, miR-135a, miR-190b, miR-205, and miR-744 and of the risk scores obtained from the Oncotype DX
® DCIS assay. These analyses revealed that the highest miRNA expression differences could be observed by combining the intermediate and high-risk groups, in comparison to the low-risk group. Our miRNA composite risk score based on the validated expression of these 5 miRNAs further highlighted the molecular difference between low- and intermediate-/high-risk groups (
p<0.0021). These findings are in agreement with the original study used to develop the Oncotype DX
® DCIS Assay (ECOG 5194) where the risk of local recurrence between the intermediate and low risk was higher than between high-risk and low-risk groups [
27,
36]. More precisely, the analyses of Solin et al. revealed that the 10-year risk of developing IBC was 10.6% for the low-risk group, 26.7% for the intermediate risk group, and 25.9% for the high-risk score group, with the highest recurrence rate for the intermediate group [
27]. Incidentally, although our sample size was small (i.e., 41 patients) and our follow-up data (i.e., 32 out of 41 patients) was generally limited to 4–8 years, we identified two patients diagnosed with DCIS who experienced ipsilateral recurrences (i.e., one patient with a DCIS recurrence and one patient with an invasive breast cancer recurrence). The patient who experienced a DCIS recurrence was initially provided a low Oncotype DX
® DCIS risk score, but classified with the 2nd most extreme decreased miRNA expression in our low score group. Additionally, the DCIS patient who experienced an invasive breast cancer recurrence and whose DCIS lesion was initially provided an intermediate Oncotype DX
® DCIS risk score obtained the 4th most extreme miRNA expression decrease in our intermediate-/high-risk score. Although our sample size was small and only identified two ipsilateral recurrences, our data suggest that the miRNA composite score may have prognostic utility beyond the Oncotype DX
® DCIS assay score, a hypothesis that will need to be evaluated in follow-up studies.
As detailed in our study, we identified and validated a subset of five miRNAs for which progressive expression downregulation was significantly associated with increased Oncotype DX
® DCIS risk scores, which could suggest that some of these miRNAs may be directly or indirectly involved in the expression regulation of some of the genes included in the Oncotype DX
® DCIS assay, but that will require further experimental confirmation. Interestingly, one of these miRNAs, miR-190b (
p=0.043), has been shown to be the most upregulated miRNA in estrogen receptor-positive cancer [
71]. Hsa-miR-30c, which was the second most downregulated miRNA in our study (
p=0.011), has been reported to be an independent predictor for benefit of endocrine therapy in patients with ER-positive breast cancers. Considering that all DCIS lesions evaluated in our study were ER positive, expression downregulation of hsa-miR-30c may potentially have both prognostic and predictive value, but will require long-term follow-up [
72]. In a recent study of ER-positive invasive breast tumors, we also identified downregulated expression of hsa-miR-30c in patient tumors correlated with subsequent metastasis, suggesting that this miRNA could provide information on the potential of DCIS lesions for progression to invasive disease [
73]. The expression of miR-744 is known to be downregulated in several cancers including breast tumors [
74].
In vitro studies evaluating overexpression of hsa-miR-744 in breast cancer cell lines and in particular ER-positive MCF-7 breast cancer cells lead to a significant inhibition of cellular proliferation. For DCIS lesions the decrease in hsa-miR-744 expression may provide a significant benefit for the cellular proliferation of DCIS cells. Interestingly, Chen et al. determined that increased expression of hsa-miR-744 in FFPE specimens from breast cancer patients was associated with chemo-resistance [
75]. Finally, multiple molecular expression studies have shown a direct relationship between hsa-miR-135a expression and various human malignancies, including breast cancer [
65,
72]. While some contrasting results have been reported, whereby hsa-miR-135a is either up or downregulated in differing cancers, hsa-miR-135a appears to function as a tumor suppressor in breast cancer and seems to be downregulated in human ER+ and triple negative (TN) breast cancers [
65,
76,
77].
It is noteworthy that 3 of the 5 miRNAs in our composite risk score, specifically miR-205, miR-190b, and miR-135a, were derived from our analysis of the correlation between their expression in the DCIS lesions and the patient’s age. The original Oncotype DX
® DCIS assay, which was established after analysis of local recurrences in 327 patients with DCIS in the ECOG 5194 study, provided recurrence risk estimates solely based on the DCIS Score [
27]. However, a more recent multivariable analysis (2018) performed on a larger cohort (Ontario cohort), which included 571 women diagnosed with DCIS found that after adjustment for clinicopathologic variables, particularly patient age, this had a larger effect on the evaluation of local recurrence risk than the DCIS score alone [
36,
78,
79]. Our findings would further confirm that patients’ age and in turn miRNA expression changes associated with age in those patients provide additional targets for the evaluation of the patient’s risk. Currently, the local recurrence risk algorithm provided by the DCIS score incorporates patient age and varies more due to patient age than the actual score, with patients under 50 reported as having a higher local recurrence risk at any score. In our study, all cases had a DCIS score reported prior to incorporation of age in recurrence risk estimates; however, our analyses would suggest that these age-related miRNA expression changes might help refine the Oncotype DX
® DCIS local recurrence risk estimates.
The most significant result drawn from this study was the highly significant decrease in expression of hsa-miR-205 (adj
p<0.00056 by RT-qPCR validation) in DCIS lesions with intermediate/high Oncotype DX
® DCIS scores. Hsa-miR-205 has already been demonstrated to confer invasive potential to DCIS cells in a breast cancer cell progression model described by Chen et al. [
78]. Hsa-miR-205 has recently been described as an oncosuppressive miRNA, because its expression is directly regulated by the tumor suppressor p53 [
78‐
80]. Mutations in p53 have been shown to inhibit the expression of hsa-miR-205, leading to enhanced cellular proliferation of breast cancer cells [
80]. Interestingly, hsa-miR-205 has also been found to target the human epidermal growth factor receptor, HER3, in human ER+ breast cancer cells [
80]. Furthermore, others have found hsa-miR-205 binding sites in the noncoding region of the Zinc Finger E-Box Binding Homeobox 1 (Zeb1) and Smad interacting protein 1 (Sip1) mRNA sequences, two key proteins, which have been implicated in epithelial–mesenchymal transition (EMT) and suggesting a potential role for DCIS to invasive breast cancer cell transition/progression [
81]. In vitro studies in MDCK–Pez cells (a canine epithelial cell line that has undergone EMT via the overexpression of protein tyrosine phosphatase Pez) further highlighted that addition of exogenous precursor hsa-miR-205 results in a phenotypic change from mesenchymal-like back to epithelial-like [
81]. Altogether, decreased expression of hsa-miR-205 is in agreement with the literature, whereby hsa-miR-205 is consistently downregulated in breast cancers [
78‐
81], suggesting that early molecular changes such as decreased expression of hsa-miR-205, as early as in DCIS lesions, may increase the likeliness of breast cancer progression. However, larger-scale and more focused studies will be required to evaluate the prognostic potential of hsa-miR-205 and other miRNAs.
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