Interobserver variability in determining MIB-1 labeling indices in oligodendrogliomas.

Several studies have shown that MIB-1 labeling indices correlate well with tumor grade and prognosis in a variety of tumor types. Several factors are responsible for some degree of variability in the determination of labeling indices. Interobserver variability is one of the factors often cited as responsible for this variability. A slide from each of 30 oligodendrogliomas, stained with MIB-1 antibody, was distributed to six pathologists. The same set of slides was reviewed by each individual. Each pathologist was instructed to determine a MIB-1 labeling index by evaluating 1,000 tumor cell nuclei from the area of the slide with the most staining. The labeling index record reflected a percentage of positive-staining tumor cells. Interobserver agreement was compared. MIB-1 labeling indices ranged from 0 to 45.7. Overall agreement was good (> or =0.75) with a concordance coefficient of 0.832 (confidence interval, 0.700 to 0.909). Variability was greater among tumors with higher labeling indices as compared with tumors with labeling indices closer to 0. The overall agreement of MIB-1 labeling indices, while not perfect, was good. The generally minor variability among observers may be related to differences in the area of the slide evaluated and in differing lower thresholds for interpreting positivity. Further improvement of concordance may theoretically be attainable by further training and discussion among observers.

Primary cutaneous diffuse large B-cell lymphoma: a clinicopathologic study of 15 cases.

Primary cutaneous diffuse large B-cell lymphoma (DLBCL) is an uncommon lymphoma. Some authors have suggested that large B-cell lymphoma can be segregated based on anatomic site, with tumors of the lower extremity being unique. We report 15 cases of primary cutaneous DLBCL. Each case was analyzed immunohistochemically using antibodies specific for CD3, CD5, CD10, CD20, bcl-2, bcl-6, and p53. Polymerase chain reaction analysis for t(14;18)(q32;q21) also was performed. There were 13 men and 2 women (median age, 64 years). Thirteen tumors were composed predominantly of centroblasts, and 2 were immunoblastic. There was a median follow-up of 72 months. Of the 4 patients with primary cutaneous DLBCL of the lower extremity (thigh, knee, leg), 2 (50%) experienced a recurrence and 1 patient died of disease. In the non-lower extremity cases, 18% (2/11) recurred and no patients died of disease. We conclude that primary cutaneous DLBCL usually occurs in elderly patients with a male predominance. Recurrences are common, but death of disease is rare.