Breast carcinoma shows various molecular characteristics and differences in biological behavior, clinical progress, and prognosis .
Precise assessment of disease characteristics and prognosis preoperatively would be of extreme importance in the diagnosis and treatment planning of breast cancer .
The role of breast MRI has been greatly increasing and it is becoming rather mandatory for preoperative assessment of patients because of its accurate valuable information regarding the characteristics, extent, and number of breast lesions.
The rapid growth of cancer is coupled with a change of both anabolism and catabolism affecting its growth and changing the intracellular and extracellular environment. Functional MR imaging techniques—such as diffusion-weighted imaging (DWI) and the measured apparent diffusion coefficient (ADC)—are helpful to detect such changes coupled with tumor proliferation .
In this study, we found that the mean ADC value of the studied breast malignant masses was 0.75 ± 0.14 × 10− 3 mm2/s.
This was comparable to the mean ADC values reported by previous studies; Kato et al.  reported that the mean ADC value of 0.894 ± 0.204 × 10− 3 mm2/s, it was 0.85 ± 0.12 × 10− 3 mm2/s in Gouhar et al.  study, 0.91 ± 0.20 × 10− 3 mm2/s in Park et al.  study, 0.93 ± 0.27 × 10− 3 mm2/s in Ulghaffara et al.  study, and 0.91 ± 0.151× 10− 3 mm2/s in Matsubayashi et al.  study.
However, Belli et al.  and Costantini et al.  reported a slightly higher mean ADC value measuring 1.02 × 10− 3 mm2/s and 1.03 × 10− 3 mm2/s, respectively.
This is probably because both Belli et al.  and Costantini et al.  studies included ductal carcinoma in situ among their investigated cases, while our study specifically included only invasive carcinomas which were more likely to have lower ADC values than the non-invasive forms.
ADC values ranged from 0.50 to 1.10 × 10− 3 mm2/s in our study and so, it did not exceed the cutoff value between benign and malignant breast lesions set by previous studies, such as Sharma et al.  who estimated a cutoff ADC value of 1.23 × 10–3 mm2/s, and Tan et al.  who found that the cutoff ADC values for benign and malignant lesions were 1.21 × 10–3 mm2/s for b = 500 s/mm2 and 1.22 × 10–3 mm2/s for b = 1000 s/mm2, respectively.
The relation between the mean ADC value and the histological grade of the detected breast carcinoma was studied in the current work. We found that there was a significant inverse relation between them, meaning that tumors with higher grade showed lower ADC values when compared with those of lower grade (p = 0.001).
This was consistent with the previous researches done by of Belli et al. , Abdel Razek et al. , Costantini et al. , and Gouhar et al.  who had reached the same conclusion.
Our results agreed also with Sharma et al. , Guo et al. , Hatakenaka et al. , and Matsubayashi et al.  who reported a significant correlation between the ADC value and the tumor cellularity.
On the other side, Park et al.  and Tan et al.  stated that no significant correlation was found between ADC values and tumor grades.
Also, Yoshikawa et al.  research which included 27 breast cancer patients, 24 of which were invasive ductal carcinoma, found that the mean ADC of breast cancer did not significantly correlate with cancer cellularity.
In our study, the mean ADC value of grade I tumors was 1.01 ± 0.06 × 10− 3 mm2/s, of grade II was 0.74 ± 0.12 × 10− 3 mm2/s, and of grade III was 0.70 ± 0.09 × 10− 3 mm2/s.
This is comparable to the results obtained by Gouhar et al.  who reported that the mean ADC values of grade I, II, and III were 0.96 ± 0.12 × 10− 3 mm2/s, 0.87 ± 0.07 × 10− 3 mm2/s, and 0.75 ± 0.12 × 10− 3 mm2/s, respectively.
However, it differs from the results obtained by Costantini et al.  who reported that the mean ADC values for grade I, II, and III tumors were 1.25 × 10− 3 mm2/s, 1.02 × 10− 3 mm2/s, and 0.92 × 10− 3 mm2/s, respectively.
This variation may be attributed to the discrepancy in the sample size and the MRI technique specially the use of different b values.
We found a significant difference between the mean ADC value of tumors of grade I and III (p = 0.001) and between grade I and II (p = 0.002). However, there was no significant difference between grades II and III (p = 0.979).
This was different from the results of Gouhar et al. , who reported that there was a significant difference in the mean ADC value of tumors of grade II and III (p = 0.003), and no significant difference between grade I and II (p = 0.054), we think the difference was due to the difference in the b values used as Gouhar et al. used only two b values (0 and 1000).
Analysis of our data revealed that using the ADC value 0.79 × 10− 3 mm2/s as a cutoff value between grade III and grades I and II has a sensitivity, specificity, PPV, NPV, and accuracy of 83.3%, 52.3%, 32.3%, 91.0%, and 58.9%, respectively. On the other hand, using the ADC value of 0.93 × 10− 3 mm2/s as a cutoff value between grade I and grades II and III has a sensitivity, specificity, PPV, NPV, and accuracy of 98%, 100%, 100%, 83.3%, and 98.2%, respectively.
Yet, we have to admit that our study was limited by the uneven distribution of the different histological grades which is due to the limited number of grade I and grade III tumors included.