Probably Benign Grading in Screening Mammograms: Review of Outcomes in a Five-year Study

Objectives: To evaluate patient outcomes after screening mammograms graded as "probably benign", and specifically to determine the corresponding frequency of false-negative diagnoses. Methods: All women with mammograms performed in the Well Women Clinics of Tung Wah Group of Hospitals (Kwong Wah Hospital and Tung Wah Eastern Hospital) from 1 January 2003 to 31 December 2007 were included in this retrospective analysis. Results: The assessment of "probably benign" was assigned to 4.8% (3182/66,362) of the screening mammograms. Among these 3182 mammograms, 27 were finally diagnosed to have cancer within two years. The percentage of cases designated as "probably benign" but that finally turned out to be malignant was 0.85% (27/3182). The pathological reports for two out of these 27 cases could not be traced. Of the available 25 cases, 17 were at stage 0, six at stage I, and two at stage IIA. None of the lesions were palpable at the time of the diagnosis and they did not have evidence of any systemic metastasis. Conclusion: At our centre, the assessment of "probably benign" on screening mammograms was on the low side compared to screening programmes elsewhere. In our study population, the percentage of those designated "probably benign" but finally turned out to be malignant was also much lower than the internationally recognised acceptable standards. In our screened population with such a diagnosis, the tumour size, lymph node status, and cancer stages were typical of lesions having a favourable prognosis.