Preoperatively diagnosed ductal carcinoma in situ (DCIS) is sometimes upstaged to invasive cancer by postoperative pathological examination. Various preoperative factors associated with upstaging to invasive cancer have been reported; however, this subject remains to be clarified. DCIS takes various forms on imaging, but many cases show non-mass-type lesions. In non-mass-type DCIS, recognizing the presence of invasion is difficult. To investigate predictors associated with upstaging to invasive cancer more precisely, we examined only non-mass-type DCIS. The present study retrospectively analyzed 101 patients diagnosed with non-mass-type DCIS preoperatively on breast biopsy at our institution between 2007 and 2017. Data were analyzed using Fisher's exact probability test and two-sample t-tests. Multivariate analysis was performed using logistic regression. The results showed that 27 patients (27%) were finally diagnosed with invasive cancer. Univariate analysis revealed abnormal result of palpation on breast examination (P=0.05), comedo necrosis (P=0.05), and HER2 status (P=0.02) as significant predictors. Multivariate analysis revealed an abnormal result of palpation as an independent predictor of invasive cancer underestimation (odds ratio 4.76; confidence interval 1.44-15.7; P=0.01). In conclusion, preoperatively diagnosed non-mass-type DCIS represented an underestimation in approximately 27% of cases. In particular, the presence of a clinically abnormal palpation increases the chance of upstaging to invasive cancer.