[Morphological features of basal-like subtype invasive carcinoma of breast]

To summarize the morphological features of basal-like subtype of invasive breast carcinoma (BLSIBC), and to look for diagnostic clues for its recognition.

Immunohistochemistry was performed in 109 cases of invasive ductal carcinoma, with CK5/6, CK14, CK8/ 18, 34betaE12, calponin, p63, CD10, ER, PR and c-erbB-2 monoclonal antibodies. Five subtypes were classified according to immunophenotypes: luminal A subtype (ER+/HER2-), luminal B subtype (ER+/ HER2+), normal breast-like subtype (ER/HER2-), HER2-overexpressing subtype and BLSIBC which was identified with at least one kind of basal-like cytokeratins or markers of myoepithelium and ER/HER2. The microscopic features of basal-like subtype were also analyzed.

The number of luminal A case was 48 (44.0%), luminal B 15 (13.8%), HER2 over-expressing 15 (13.6%), normal breast-like 10 (9.1%), basal-like subtype 19 (17.4%). Besides, the other two cases expressed c-erbB-2 or/and ER plus markers for myoepithelium, thus were excluded from all the five mentioned subtypes. Of the 19 basal-like subtype, CK5/6 was expressed in 16 cases, CK8/18 in 17 cases, CK14 in 11 cases, 34betaE12 in 18 cases, p63 in 5 cases, CD10 in 6 cases, and calponin in 1 case. The diameter of the BLSIBC cases was 1.2-7 cm (averagely 3.9 cm) , and in 6 cases, the tumor diameter was >5 cm. Only one case displayed extensive in situ component, 9 cases were grade 2, and 9 cases were grade 3. Compared to non basal subtype, there were significantly more high grade cases (P <0.01). The morphological features of basal-like subtype were summarized as the followings: pushing margin (13 cases), lymphocytic tissue hyperplasia (18 cases), nest or sheet arrangement (18 cases), nucleus grade 3 and scattered giant or bizarre nuclei (17 cases), syncytial growth (7 cases), and comedo-like necrosis (17 cases). The frequency of these features were significantly more common than non basal subtype (P <0.01).

The morphologic diagnostic features of BLSIBC are pushing margins, lymphocyte infiltration, comedo-like necrosis, gigantic cell and syncytial growth.