Microinvasive breast carcinoma - Clinicopathologic analysis of a single institution experience

BACKGROUND. Microinvasive breast carcinoma (MIC) has a good prognosis but s pecific definitions have varied in the past, making the clinical significan ce of MIC a subject of debate. METHODS. Microscopic slides of 59 cases of breast carcinoma originally diag nosed as MIC were reviewed retrospectively. Histologic parameters were corr elated with clinical findings and outcome to define diagnostic criteria bet ter. RESULTS, On review, the 59 cases were recategorized as follows: pure DCIS ( N = 16), DCIS with foci equivocal for microinvasion (N = 7), DCIS with grea ter than or equal to 1 focus of microinvasion (N = 11), T1 invasive carcino mas with greater than or equal to 90% DCIS (N = 18), and T1 tumors with < 9 0% DCIS (N = 7). The MIC cases in the current study averaged 3 separate foc i of early infiltration outside the basement membrane, each one not > 1.0 m m. The mean follow-up was 95 months. Six patients (10%) had only local recu rrence: 1 case each in patients with equivocal microinvasion, microinvasion , and T1 tumors with < 90% DCIS and 3 cases among the patients with T1 tumo rs with greater than or equal to 90% DCIS. Four patients, all with T1 tumor s with > 90% DCIS, had distant failure (7%). In the MIC group, only one pat ient developed a local recurrence after breast conservation. No patient had axillary lymph node metastasis. For the entire series, factors associated with local recurrence were younger age, breast conservation versus mastecto my, and close surgical margins. The only factor associated with distant fai lure was the size of the DCIS component. Seven patients with T1 tumors with < 90% DCIS experienced local or distant failure and 5 of these (71%) devel oped progressive disease or died of disease. AU other patients who develope d a recurrence were disease free at last follow-up. In a retrospective seri es, poorer outcome in carcinomas with < 90% DCIS may be related to the grea ter likelihood of missed larger areas of invasive carcinoma. Therefore, met iculous and extensive sampling of these carcinomas is required. CONCLUSIONS. MIC as defined has a good prognosis. It has a different biolog y than T1 invasive carcinoma with greater than or equal to 90% DCIS, which may progress and cause death. Large tumors with multiple foci of microinvas ion may have metastatic potential. Cancer 2000;88:1403-9. (C) 2000 American Cancer Society.