Well that's confusing.

You need to talk to somebody who can provide clarification.

The issue, I think, is that there can be a fine line between a low grade DCIS diagnosis vs. a diagnosis of a benign but high risk condition.

My interpretation is that perhaps your biopsy sample was at one point thought to be one, and then revised to be the other. What's unclear is which is the final diagnosis. Did the 'Addendum' come after the previous 'Final Diagnosis' or is the 'Final Diagnosis' a conclusion at the end of the 'Addendum'?

Also confusing is that normally when there is this uncertainty, it is between DCIS and ADH, whereas in your case it states "usual ductal hyperplasia and adenosis with dystrophic calcifications", which is a further one step removed (towards the benign side) from DCIS. Confusing low grade DCIS with ADH is common (well maybe not common but it certainly can happen) but confusing DCIS with usual ductal hyperplasia seems odd.

In any case, it's likely that either a lumpectomy or excisional biopsy (basically the same surgery but done before a final diagnosis is made) would be recommended. In the case of a DCIS diagnosis, a lumpectomy would be done to ensure that all the DCIS is removed. In the case of ADH or a similar high risk condition, an excisional biopsy would be recommended to ensure that there isn't any DCIS hiding in the mix, which does something happen. In both cases, a sentinel node biopsy would not be required. So the surgery is the same either way.

Some website info that might explain why there is confusion:

Ductal Carcinoma in Situ of the Breast

Differential Diagnosis

Low Grade DCIS vs. Atypical Ductal Hyperplasia (ADH)

• Low grade DCIS requires all of the following
  • Complete filling of ducts by cells with uniform round nuclei without substantial overlap
  • No streaming of cells
  • No columnar cell population
  • Sharply punched out cribriform spaces, microacini or bulbous papillae
    • Solid low grade DCIS is rare but must be excluded before using this feature to diagnose ADH
  • Size over 2-3 mm and involvement of at least two ducts

And from the BCO site; here you can see what usual ductal hyperplasia, ADH and DCIS would look like under a microscope (the 3 images that I've circled in blue):