唐平教授点评：

From the pictures, it looks like a spindle cell tumors with cellular areas and some myxoid areas, from cytology and the growth pattern, it should be malignant, my top pick will be metaplastic carcinoma, of course need to be confirm by IHC and also r/o malignant Phyllodes tumors.

I am glad this is coming up before my talk on spindle cell lesion of the breast later month

In general, spindle cell lesions of the breast are metaplastic carcinomas unless proved otherwise, they are always cytokeratin positive, but the stain can be focal and weak, so need to use a panel of CK markers instead of just one or two. P63 in positive in about 70% of metaplastic carcinoma as well.

The leading differential diagnosis is malignant phyllodes tumor, which is much less common, compared to metaplastic CA, and should be CK negative

The best way to differentiate these two entities are sampling extensively, MC will likely to have some epithelial areas, and PT will likely to have some leaf-like areas, then IHC can be helpful too.

Other differential including angiosarcoma, especially post radiation therapy, among others.

读片会讨论意见：

1.      脂肪肉瘤，待标记

2.         Spindle cell carcinoma vs sarcoma. Need IHC. Small focus of low grade DCIS at the edge.

3.      high grade metaplastic with DCIS

4.      化生性癌（含脂肪肉瘤样成分）

5.      （右乳）化生性癌，见有导管内癌，染免疫组化排除恶性叶状肿瘤伴导管内癌

6.      乳腺恶性肿瘤，首先考虑化生性癌

7.         Metaplastic (sarcomatoid) carcinoma, with associated DCIS

8.      低级别梭形细胞化生性癌

9.      梭形细胞癌

10.  化生性癌

11.  化生癌（治疗后反应）

12.  脂肪肉瘤

13.  化生性癌伴导管内癌。

 恶性。肿瘤细胞和间质均特殊。鉴别：

1、化生性癌（梭形细胞癌+产基质癌）

2、恶性叶状肿瘤

3、软组织肉瘤