Mammary Paget's disease: evidence of diverse origin of the disease with a subgroup of Paget's disease developing from the superficial portion of lactiferous duct and a discontinuous pattern of tumor spread.

The pattern of spread of intraductal carcinoma associated with mammary Paget's disease has not been well studied. The purpose of this study was to examine the site of origin and the pattern of tumor spread with a three-dimensional view by serial sectioning of the tissue blocks from 19 cases of Paget's disease. Intraductal carcinoma in the superficial portion of the lactiferous ducts was seen in continuity with the overlying epidermis with Paget's disease in all 19 cases. In seven cases that had adequate tissue sampling, five showed a continuous pattern of the intraductal carcinoma within the superficial as well as the deep breast tissue. In the remaining two cases, a portion of benign duct was identified between the intraductal carcinoma in the superficial lactiferous duct and the deep breast tissue. This discontinuous pattern of spread of the intraductal carcinoma was also identified in the foci of carcinoma in deep tissue. In the five cases in which the tumor involved the skin and only the superficial portions of the lactiferous duct, the leading edge of the intraductal carcinoma was seen orientated in the direction of the nipple towards the deep breast tissue. Our study of Paget's disease demonstrated that in addition to tumor spread along the lactiferous ducts from intraductal carcinoma in the deep tissue towards the nipple, there was a group of Paget's disease arising from the nipple. These lesions included: (i) lesions limited to the areolar tissue; and (ii) lesions with intraductal carcinoma involving the duct system in both superficial and deep breast tissue with and, possibly, without skip areas pattern of spread. Although certain cases of Paget's disease may appear superficial, an independent associated carcinoma in deep breast tissue has to be ruled out.