Minimal breast cancer: evaluation of histology and biological marker expression.

Ninety-eight minimal breast cancers (MBCs) diagnosed between 1975 and 1990, and all originally considered to be invasive were found, on review, to form three groups: (a) 28 predominantly invasive carcinomas < or = 10 mm ('predominant invasive'); (b) 48 predominantly ductal carcinoma in situ (DCIS) lesions with definite foci of invasion each < or = 10 mm ('predominant DCIS'); and (c) 22 DCIS without evidence of invasion ('pure DCIS'). Tumour histology and immunohistochemical expression of Ki-67, c-erbB2, p53, oestrogen receptor (ER), progesterone receptor (PR), and Bcl-2 were compared. The major finding was the contrasting features in the two invasive groups, with significant differences in their extent of invasion (P < 0.0001), tumour grade (P = 0.03), DCIS type (P = 0.008) and in marker expression. In the predominant invasive group, the infiltrative component was usually greater than 5 mm, low-grade and associated with well-differentiated DCIS. Expression of Ki-67, c-erbB2 and p53 was generally low, and that of ER, PR and Bcl-2 high. The predominant DCIS group in contrast had a much smaller, commonly high-grade, invasive component, usually with poorly differentiated DCIS and the reverse pattern of marker expression. Although not significant, survival of patients in the predominant invasive group was slightly better. These findings suggest that invasive MBCs should perhaps be treated as separate entities, in order to aid more appropriate selection of treatment.