Cancer larger than on mammo

I just had surgery on a 1.6 mucinous cancer lesion that upon removal turned out to be more of the size of 6cm.  There was no lymph node involvement. But superior margin was not clear. Is superior the upper portion of breast?  The world renowned surgeon wants to go in and take 1 cm more to get a clear margin.
Does this size tumor still OK for lumpectomy.  My breast hardly looks different which is a blessing.  I do want to be safe though. The tumor is graded 4 on Bloom scale, no in situ carcinoma and only focally lymphovascular on one specimin.  I am meeting with a Breast oncolgist for her opinion.  the tumor was called low grade and low mitosity.  Of course this is troubling that it is larger but I am hopeful.  Thoughts?
Wendy

[CCF-RN,MSN-rf]

Dear Wendith:  The superior margin refers to the top of the tumor, which would be toward the top of the breast.   A lumpectomy can be performed with any size tumor, provided there is only one tumor, there are adequate margins, and there is enough remaining breast tissue to produce a cosmetically good result.  Of course, any time a lumpectomy is performed, it should be followed by radiation therapy.