Expression of p40 and laminin 332 in metaplastic spindle cell carcinoma of the breast compared with other malignant spindle cell tumours.

AIMS: To determine the use of p40 and laminin 332 (LN332) immunostains for diagnosing metaplastic carcinoma by studying the expression of these and other routine markers in spindle cell metaplastic carcinomas and other malignant spindle cell tumours.

METHODS: We identified cases of spindle cell metaplastic carcinoma (n=36) and other atypical/malignant spindle cell tumours, including 20 phyllodes tumours (14 borderline, six malignant) and 23 spindle cell sarcomas (three primary to breast). Immunohistochemical staining was performed for p40 and two LN332 chains, β3 (kalinin B1) and γ2 (lamC2). The expression of these markers was compared with p63 and cytokeratins.

RESULTS: p40 and p63 expression was seen in 21 of 36 (58.3%) and 33 of 36 (91.7%) metaplastic carcinomas, respectively. No phyllodes tumours showed stromal expression of p40 or p63. One of 23 (4.3%) sarcomas showed focal weak p63 staining. LamC2 and kalinin B1 expression was seen in 28 of 36 (77.8%) and 26 of 36 (72.2%) metaplastic carcinomas, respectively. LamC2 and kalinin B1 each showed positive stromal cell expression in two of 20 (10%) phyllodes tumours. No sarcomas showed staining with lamC2. Kalinin B1 staining was seen in 17 of 23 (73.9%) sarcomas, including two of three primary breast sarcomas. Cytokeratin expression was seen in 32 of 36 (88.9%) metaplastic carcinomas and diffuse staining was most often seen in 34βE12 and CK5.

CONCLUSIONS: The diagnostic value of relatively novel markers p40 and LN332 was found to be less than that of routinely used markers (p63 and cytokeratins). p40 proved to be a specific marker but lacked the sensitivity of p63, while LN332 showed staining in a significant proportion of phyllodes tumours and sarcomas.