Pitfalls in breast cancer diagnosis concern interpretation of frozen section as well as gross and histological examination. Problems in frozen section diagnosis may be created either by overdiagnosis which is the commonest, or by under-diagnosis. Benign lesions overdiagnosed as carcinoma are florid epithelial hyperplasia in a fibroadenoma, especially when a small piece of tissue is available, a chronic inflammatory mass, a papilloma and sclerosing adenosis. The latter is the lesion most commonly overdiagnosed in frozen section. Underdiagnosis of malignant lesions includes in situ carcinoma most commonly the LCIS, infiltrating lobular carcinoma and tubular carcinoma. In gross and conventional histologic examination, a variety of benign lesions can mimic invasive breast cancer. Some benign lesions possess imaging and/or gross features suggestive of malignancy but usually do not present diagnostic difficulties after microscopic examination such as surgical scars, fat necrosis, granular cell tumors. Other benign breast lesions have a suspicious radiographic and/or macroscopic appearance and also have microscopic features confused with those of invasive carcinoma e.g. radial scars, complex sclerosing lesions, mucocele-like lesions. Finally, benign lesions not associated with radiographic or macroscopic changes suggesting malignancy, possess worrisome microscopic features (e.g. microglandular adenosis). On the other hand, some examples of in situ breast carcinoma may have microscopic patterns simulating invasive carcinoma, for instance LCIS involving areas of sclerosing adenosis. It is also important to consider the possibility of eronneous diagnosis after needling procedures which can induce a number of artefacts in subsequent breast excision specimens. These include displacement of benign ductal epithelium or DCIS cells into the stroma or into vascular spaces. For minimizing pitfalls in breast cancer diagnosis it is of paramount importance for the pathologist to be provided by clinical data. Moreover the same pathologist should perform the naked-eye pathology and microscopic examination.

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