Thank all of you for reading the case and writing your diagnosis here. Most of you have the correct or almost right interpretation or differential diagnosis.

This is a microglandular adenosis  (MGA) case. The main differential dx contain tubular carcinoma (TC) and other adenosis and its variants. The diagnosis is not very difficult based on the morphology if you see few cases already. Histologically, MGA consists small round glands with open lumens, distributed mostly randomly in a hypocellular dense collagenous or fatty stroma. The glands are lined by a single layer of (flat to) uniform cuboidal epithelial cells and completely invested by a basement membrane (TC with no BM). The Lumen contains PAS+ eosinophilic secretion. You should make the dx if you know these morphologic features well. Please compare the morphologic features of this case with that of my above TC cases.

IHC stains can help you. I summaried a brief table below.

*Collagen IV, laminin, reticulin

Very glad to see that some of you have noted the presense of cellular atypia. Focal areas (last 4 photos) show varied gland configuration or irregularity of the glands. Some glans lack secretion and the lumens are obscured by celluar prolifearion. The cells demonstrate mild-moderate nuclear pleomorphism and prominent nucleoli. So the case was dianosed MGA with focal atypia or atypical MGA (AMGA).

MGA is an extremely rare benign breast lesion. 108 cases were originally diagnosed as MGA in M.D Anderson Cancer Center (one of the largest cancer center in the US) from 1983 to 2007. Of the 108 cases, 65 cases had available  materials for review. 11 of 65 cases qualified to have MGA component. Myoepithelial layers was detected in other 54 cases and they were reclassified as adenosis.  Now you know the true MGA case is rare and rare. The hospital I currently work is one of the largest gyn and breast center in the US. Only one MGA case was diagnosed in the past three years. The current case is the one when I worked at AFIP.

The lesion is spectrum of glandular proliferations ranging from uncomplicated MGA to MGA with atypia to MGA associated carcinoma (MGACA). For difficult cases IHC stains for Ki67 and p53 can be helpful.

Ki67: MGA <3%; AMGA 5-10; MGACA>30%

p53: MGA<3%; AMGA 5-10%; MGACA>30%

I think the percentage is just for reference and histologic features are the key for diagnosis.

Useful reference:

1. Khalifeh IM etal. Clinical, histopathologic, and immunihistochemical features .... Am J Surg pathol 2008;32:544-552.

2. Koenig C et al. Carcinoma arising in microglandular adenosis: an immunohistochemical analysis....Int J Surg Pathol 2000;8:303-315.

Just came back from China and feel tired. I put the case here three weeks ago and have to complete it . Sorry for the delay.

Thanks,

cqz