Vitamin D Receptor Expression in Invasive Breast Tumors and Breast Cancer Survival

Linnea Huss; Salma Tunå Butt; Signe Borgquist; Karin Elebro; Malte Sandsveden; Ann Rosendahl; Jonas Manjer

Disclosures

Breast Cancer Res. 2019;21(84) 

In This Article

Results

Patterns of VDR Expression

VDR was expressed almost exclusively in tumor cells as compared to surrounding cells within the TMA core. When cancer in situ cells were noted in the same core as invasive tumor cells, in situ cells were differently stained compared to invasive cells. Invasive cancer had a more intense stain and a larger fraction of nuclear staining than cancer in situ cells (Figure 2A). As only invasive cancer cells were scored for this project, such differences were not systematically recorded.

VDR was expressed in all compartments of cancer cells (Figure 2B). Nuclear VDR expression was assessable in 678 (94.4%) of tissue core pairs, and cytoplasmic VDR expression as regards to fraction and intensity was scored in 679 (94.6%) of available tumors. Due to difficulties in distinguishing VDR expression between nuclear membrane and cellular membrane, there was a high percentage of discordance between the first and second rounds of scoring at these compartments (14.1% of nuclear membrane fraction and 30.1% of cellular membrane fraction).

Staining patterns of nuclear VDR fraction are illustrated in Figure 2C–E. Percentages of highly intense stain in nucleus covaried highly with the fraction of nuclear stain and were therefore not included in further analyses. Distribution of nuclear fraction is presented in Table 1.

The vast majority of tumors 624 (91.9%) expressed cytoplasmic VDR to a high fraction (76–100%) of cells. There was a wider distribution of intensity: no stain (n = 7, 1.0%), low intensity (n = 26, 3.6%), moderate intensity (n = 174, 24.2%), and high intensity (n = 472, 65.7%) (Figure 2F–H). Distribution of scores of cytoplasmic VDR expression is presented in Additional file 1: Table S1.

Covariation of VDR Expression and Tumor Characteristics

Distribution of patient and tumor characteristics in relation to nuclear VDR fraction is presented in Table 1. There was a statistically significant covariation between VDR negativity and many tumor characteristics associated with poor prognosis: large tumor size (p = 0.002), high Nottingham grade (p < 0.001), negative ER status (p < 0.001), negative PgR status (p < 0.001), and high Ki67 expression (p < 0.001). There was also a statistically significant covariation between histological type and VDR expression, where negative tumors more often were considered ductal (p < 0.001). When molecular subtypes were compared, it was noted that only 6.6% of Luminal A-like tumors had a negative VDR expression in the nuclei as compared to 25.6% among Luminal B-like tumors, and 78.4% among triple-negative tumors.

A similar pattern was observed when the distribution of patient and tumor characteristics in relation to cytoplasmic VDR score was analyzed (Additional file 1: Table S1). One difference was that cytoplasmic VDR score also showed statistically significant covariation with HER2, as no tumors within the group of low cytoplasmic score (0–6) were considered HER2 positive (p = 0.008).

Covariation of VDR Expression and Breast Cancer Treatment

Mastectomies were performed more often on VDR-negative tumors (55%) compared to VDR-positive tumors (41%). The postoperative treatment conference recommended adjuvant endocrine therapy for a smaller proportion and chemotherapy for a larger proportion of patients with VDR-negative tumors compared to VDR-positive tumors. A similar pattern was seen when cytoplasmic VDR score was compared to treatment factors.

VDR Expression in Relation to Breast Cancer Mortality

Mean follow-up was 11.5 years with a standard deviation (SD) of 5.2 years. A Kaplan-Meier analysis confirmed proportional hazards as shown in Figure 3. Both crude and adjusted analyses showed a statistically significant association between nuclear VDR positivity (a fraction above 10% of stained nuclei) and a low risk of breast cancer-associated death (HR = 0.56, 0.34–0.91) adjusted analysis) (Table 2). The complete case analysis showed similar but not statistically significant results (0.61, 0.35–1.05). Also, similar but not statistically significant results were seen when nuclear VDR fractions 11–50% (0.54, 0.32–0.89) and nuclear VDR fractions 51–100% (0.66, 0.34–1.28) were compared individually to nuclear VDR fraction below 10%. It was also noted that the difference in HR between nuclear VDR fractions 11–50% and nuclear VDR fractions 51–100% was small.

Figure 3.

Kaplan-Meier showing breast cancer-specific survival

As regards to HRs calculated for different cytoplasmic VDR scores, they showed similar results as for nuclear VDR expression, i.e., more VDR expression was associated with decreased risk of breast cancer death, but not statistically significant when adjusted (0.59, 0.30–1.16) (Table 2).

VDR Expression in Relation to Breast Cancer Mortality Stratified by Molecular Subtypes

HRs for breast cancer death calculated in groups stratified by molecular subtypes are presented in Table 3. There was a statistically significant association between VDR expression and BCM within the Luminal B-like tumors as nuclear VDR positivity was associated with a decreased risk of breast cancer death (0.37, 0.18–0.77). Also, there seemed to be a possible association within the Luminal A-like molecular subtype and reduced risk of breast cancer death, but this association did not reach statistical significance (0.76, 0.32–2.53). For HER2-positive and triple-negative molecular subtypes, no statistically significant results were observed.

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