To determine whether T2 signal intensity, necrosis, and ADC values are associated
with Ki-67 in patients with Estrogen Receptor (ER)-positive and Human epidermal growth
factor receptor type 2 (HER2)-negative invasive ductal carcinoma (IDC). Between March
2012 and February 2013, one hundred eighty seven women with ER-positive and HER2-negative
IDC who underwent breast MRI and subsequent surgery were included. Intratumoral signal
intensity was evaluated based on a combination of T2-weighted (low or equal, high,
or very high) and contrast-enhanced MR images (enhancement or not). Necrosis was defined
as very high T2 and no enhancement. Using the analysis of variance and pairwise t
-test, a model based on intratumoral signal intensity was developed to assess Ki-67
of the surgical specimen. Inter-observer agreement for the developed model was analyzed.
Conventional mean and minimum apparent diffusion coefficient (ADC) measurements were
performed and correlated with Ki-67. As the grade of the developed model increased
(Grade I: low or equal T2, Grade II: high T2, or necrosis < 50%, Grade III: necrosis
≥ 50%), mean Ki-67 significantly increased (Grade I to III: 12.5%, 17.6%, 45.0%, respectively;
P < 0.001). Good inter-observer agreement was found for the model (κ = 0.846, P
< 0.001). ADC did not show significant correlations with Ki-67 (Pearson’s correlation
coefficient, 0.140 [ P = 0.057] for mean ADC; −0.079 [ P = 0.284] for minimum ADC).
Intratumoral signal intensity but not ADC was associated with Ki-67 in patients with
ER-positive and HER2-negative IDC.