Correlation of the apparent diffusion coefficiency values on diffusion-weighted imaging with prognostic factors for breast cancer

Objective

The aim of this study was to correlate the apparent diffusion coefficient (ADC) value of breast cancer with prognostic factors.

Methods

335 patients with invasive ductal carcinoma not otherwise specified (IDC NOS) and ductal carcinoma in situ (DCIS) who underwent breast MRI with diffusion-weighted imaging were included in this study. ADC of breast cancer was calculated using two b factors (0 and 1000 s mm^–2). Mean ADCs of IDC NOS and DCIS were compared and evaluated. Among cases of IDC NOS, mean ADCs were compared with lymph node status, size and immunochemical prognostic factors using Student''s t-test. ADC was also correlated with histological grade using the Kruskal–Wallis test.

Results

Mean ADC of IDC NOS was significantly lower than that of DCIS (p<0.001). However, the mean ADC of histological grade of IDC NOS was not significantly different (p=0.564). Mean ADC of oestrogen receptor (ER)-positive or progesterone receptor (PR)-positive cancer was significantly lower than that of ER-negative or PR-negative cancer (p=0.003 vs p=0.032). Mean ADC of Ki-67 index-positive cancer was significantly lower than that of Ki-67 index-negative cancer (p=0.028). Mean ADC values of cancers with increased microvascular density (MVD) were significantly lower than those of cancer with no MVD increase (p=0.009). No correlations were observed between mean ADC value and human growth factor receptor 2 expression, tumour size and lymph node metastasis.

Conclusion

Low ADC value was correlated with positive expression of ER, PR, increased Ki-67 index, and increased MVD of breast cancer.Breast MRI is an established supplemental technique to mammography and ultrasonography for evaluation of suspicious breast lesions. Diffusion-weighted MRI (DWI) has recently been integrated into the standard breast MRI for discrimination of benign and malignant breast lesions obtained with dynamic contrast-enhanced MRI 1-13]. DWI is a non-invasive technique that represents the biological character of the mainly Brownian movement of protons in bulk water molecules in vivo. Apparent diffusion coefficient (ADC) values are quantified by measurement of mean diffusivity along three orthogonal directions, which are affected by cellularity of the tissue, fluid viscosity, membrane permeability and blood flow 7,9-11]. Microstructural characteristics, including water diffusion and blood microcirculations in capillary networks, were associated with ADC value. Decreased movement of molecules in highly cellular tissue showed correlation with a low ADC value 3,4]. Several studies of DWI of the breast have reported significantly lower ADC values in malignant tumours, compared with benign breast lesions and normal tissue 1-3,5-11,14]. Classic prognostic markers, including tumour size and grade, and lymph node status in patients with breast cancer, and molecular markers, including oestrogen receptor (ER), progesterone receptor (PR), Ki-67 index, human growth factor receptor 2 (HER2) protein and angiogenic molecular markers, have been reported 1,15,16]. Few studies have examined the correlation between ADC values and prognostic factors 1,8]. The purpose of this study is to compare ADC values of DWI of breast cancer with prognostic factors.