"Revertant" mammary solid papillary carcinoma in lymph node metastasis

A case of invasive carcinoma of mixed papillary and not otherwise specified ductal type with areas of solid papillary ductal carcinoma in situ(DCIS) is reported. The solid papillary areas were predominantly of low nuclear grade, but a small area of intermediate-grade solid papillary neoplasm was also seen within the tumor, together with an area suggestive of microinvasion. The massive regional nodal tumor load consisted of invasive papillary carcinoma and revertant low-grade solid papillary carcinoma with no myoepithelial cells around the circumscribed solid papillary areas. This is the first report of a solid papillary pattern simulating intraductal carcinoma in lymph nodes, and the first time that a solid papillary carcinoma is reported in association with invasive papillary carcinoma. The case suggests that mammary carcinomas with a solid papillary pattern may sometimes be of higher grade than usual, and do not always represent a DCIS, but may be invasive.