Hi,
Atypical ductal hyperplasia is what is called a "pre-malignant" condition. This means that with time, patients having this condition eventually progress into outright carcinoma. So having this condition alone may already warrant excision of the lump or lesion.
However, this is not the only finding that the pathologist was concerned about. He mentions "two small tubular proliferations" with a high probability of low grade carcinoma. Since the pathologist who originally read this slide is not sure of his finding, it might be prudent to have it reviewed by another pathologist, because there is a possibility that those tubular proliferations are indeed, cancer, albeit of a low grade variety (probably carcinoma in situ).
If a diagnosis of cancer is confirmed on slide review by another pathologist, then the sentinel lymph node biopsy would become the appropriate next step.
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