Women with nonpalpable breast masses are at a high risk of developing breast cancer (BC) due to misdiagnosis during the follow-up period.A total of 40,334 women were divided into palpable and nonpalpable breast mass groups. We assessed the risk factors for cancer development in patients with nonpalpable breast masses during a 1-year follow-up period.Of the 1335 patients in the nonpalpable breast mass group, we found 50 patients of BC, of which 35 patients accepted surgery and were confirmed with biopsy at the beginning of the study. The remaining 15 (1.1%) were diagnosed with BC during follow-up, and included 10 in situ and 5 invasive carcinomas. Four of the 10 patients in the in situ subgroup, and 2 out of the 5 in the invasive subgroup were overweight (Body mass index > 24 kg/m). Nine in situ BC patients had breast-conserving surgery, 1 had a mastectomy. No patient in the in situ group received chemotherapy or radiotherapy. All 5 patients with invasive disease received 6 cycles of chemotherapy. Only 3 (20%) of the 15 patients with BC had a positive family history. We found 131 BC cases, including BC detected during screening (81) and follow-up (50). The incidence of BC was 240.2 per 100,000 inhabitants.Patients with nonpalpable breast masses require regular follow-up as they have a high risk of cancer occurrence. Regular follow-up can lead to early diagnosis and effective treatment of these early-stage BC patients.