Background: Microinvasive carcinoma of the cervix (MIC) has been poorly defined in the past and is still a focus of persistent controversy. In 1985, the International Federation of Gynecology and Obstetrics (FIGO) defined Stage IA as "preclinical invasive carcinoma, diagnosed by microscopy only," subdividing it into Stage IA1 or "minimal microscopic stromal invasion," and Stage IA2 or "tumor with invasive component 5 mm or less in depth taken from the base of the epithelium and 7 mm or less in horizontal spread." In 1974, the Society of Gynecologic Oncologists (SGO) defined MIC as any lesion with a depth of invasion of 3 mm or less from the base of the epithelium, without lymphatic or vascular space invasion.
Methods: To assess the risk of lymph node metastasis and treatment failures, pathologic material and clinical data on 370 patients with Stage I carcinoma of the cervix, who were treated by radical hysterectomy and pelvic-aortic node dissection, were reviewed. Histopathologic analysis of tumors was based on a uniform format, including measurement of the maximum depth of invasion, the width and length of the horizontal tumor spread, invasive growth pattern, cell type, tumor grade, and lymphatic or vascular space involvement.
Results: Of the 370 patients, 110 had a depth of invasion of 5 mm or less. Of these, 54 patients fulfilled the SGO definition of MIC; 42, the new FIGO Stage IA2 definition; and 27, both definitions. None of the patients with MIC, as defined by either the SGO or the new FIGO Stage IA2, had lymph node metastases or tumor recurrence. These data support the conclusion that MIC, defined by either the SGO or FIGO definitions, have a low risk for lymph node metastasis or recurrent carcinoma. A review of the literature indicated a recurrence rate for Stage IA2 of 4.2%. In addition to depth of invasion, lymph vascular space invasion is a better predictor of lymph node metastasis and recurrence than the surface dimension.
Conclusions: The authors recommend adoption of the SGO definition of MIC. Patients with a depth of invasion of 3 mm or less without lymph vascular space invasion safely can be treated conservatively.