Abstract Background: Standard means in breast cancer follow-up include clinical examination and mammography for the detection of local recurrences. Additional test will only be conducted if there are unclear or suspicious findings. Ultrasound has not yet been established as a routine method for breast cancer follow-up care. Our study evaluates the diagnostic efficacy of breast ultrasound in detecting occult malignancies. Moreover, we analyzed the effect of false positive findings resulting in additional examinations and biopsies, and we conducted a benefit-cost-analysis and a questioning of the affected patients.Materials and Methods: A total of 879 eligible patients who were seen at the University Hospital of Saarland for the purpose of breast cancer follow-up were recruited between October 2004 and January 2006. All patients received clinical examination and mammography and were then divided into 2 groups. Group 1 (n=703) were clinically and mammographically asymptomatic patients. Group 2 (n=176) had abnormalities either in palpation or mammography. All patients received additional ultrasound in order to detect occult malignancies. Both groups were analyzed with respect to the diagnostic value of additional ultrasound, the rate of additional examinations and biopsies, the extra costs and the individual stress as experienced by the patient.Results: In group 1 (asymptomatic patients) 10 occult malignancies were detected due to the additional ultrasound examination, i.e. one diagnosed malignancy in 70 examined patients (detection rate 1.4%). By reason of false positive ultrasound results, 65 additional control-ultrasounds, 14 additional MRI examinations and finally 22 biopsies of benign lesions were unnecessarily conducted. Weighing in the total costs for ultrasound, MRI and biopsy, an amount of 4150€ (5290$) was spent to find one additional cancer.In group 2, apart from the symptomatic lesions, 3 occult malignancies were exclusively identified due to the ultrasound examination (detection rate 1.7%). On the other hand, false positive ultrasound results caused 7 additional control-ultrasounds, 14 additional MRIs and 11 biopsies of benign lesions. Hence, an amount of 4410€ (5620$) was spent to identify one additional malignancy by the means of additional ultrasound in this group.Overall, 50 patients (5.7%) received biopsy due to false positive results either in ultrasound or mammography, but these patients claimed on questioning not to feel “troubled and anxious”, but “saver and more carefully looked after”.Discussion: Regarding our results, we strongly recommend the routine use of ultrasound in breast cancer follow-up for both, asymptomatic and symptomatic, women, as occult malignancies can be identified cost-efficiently, although additional ultrasound may also result in higher false positive findings. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5027.