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As our understanding of the biology of breast cancer evolves, we recognize that there are many different types of histologically distinct cancers. Breast cancer is ahead of many other solid organ malignancies in our understanding about different tumor biologies. We routinely differentiate breast cancers based on histology between invasive ductal carcinoma and invasive lobular carcinoma. We also divide breast cancers into approximated subtypes based on their hormone receptor status (estrogen and progesterone) as well as HER-2/neu status.

There are some other breast histologies that are not as common as invasive ductal and invasive lobular carcinomas. All practitioners caring for patients with breast complaints should be aware of these unusual histologies and know how to identify them as well as where to look for guidance in treating them. Recognition of these unusual histologies will allow surgeons to recommend appropriate treatment. It will also aid in counseling patients regarding the prognosis based on the best information available.

This chapter includes unusual histologies which may be more challenging to recognize and manage partly because of their infrequent occurrence. The surgeon seeing patients with breast complaints should be familiar with these lesions in order to ensure the appropriate diagnostic evaluation and management. Accurate diagnosis is highly dependent on the availability of other specialists in the multidisciplinary team (pathologists, radiologists, medical oncologists) who can aid in the evaluation and treatment of patients with these unusual tumor types. Table 74-1 provides a summary of key facts and management of the histologies covered in this chapter.

TABLE 74-1

Unusual Breast Histologies

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