Ki67 and MIB1 monoclonal antibodies are directed against different epitopes of the same proliferation-related antigen. Whereas Ki67 works only on frozen sections, MIB1 may be used also on fixed sections. The authors immunostained a series of 40 breast carcinomas with MIB1 and Ki67 antibodies on serial frozen sections and on fixed material. The Ki67 labeling index (LI) was 12.9 +/- 8.9 and 12 (mean +/- SD and median, respectively). MIB1 LI was 21.2 +/- 11.9 and 19.5 on frozen sections and 24 +/- 15.2 and 21.5 on fixed sections (mean +/- SD and median, respectively). Ki67 LI and MIB1 LI on frozen and fixed sections were strictly correlated (P < .001). The results are in keeping with the reported coincidental nuclear staining pattern of Ki67 and MIB1, but the mean and median values of MIB1 LI are almost twice the values of Ki67 LI. The cut-off values to define high and low proliferative activity with the two antibodies are therefore different. The differences in immunolabeling may be due to better survival of the MIB1 epitope in freezing and acetone fixation or to differing accessibilities of the MIB1 and Ki67 epitopes during the cell cycle due to molecular conformational modifications. The MIB1 monoclonal antibody is a reasonable substitute for the Ki67 monoclonal antibody. The advantages of MIB1 immunostaining on paraffin sections include the feasibility of retrospective studies and of obtaining clear morphologic specimens that are optimal for use with computer-assisted image analysis systems. Our image-processing system allows automatic nuclear counting, detects positive nuclei and measures their staining intensity.

A new type of ground-glass hepatocyte is described. The appearance is due to pale, homogeneous, weakly eosinophilic inclusions filling a portion of or the entire hepatocytic cytoplasm. On haematoyxlin and eosin stained sections, these cells closely resemble ground-glass hepatocytes described in other conditions. However, they are negative on special stains for HBsAg and on PAS staining. Immunohistochemically, they reveal a selective and exclusive positivity for fibrinogen. On electron microscopy, the immunoreactive fibrinogen appears as amorphous, fluffy or granular material within dilated cisternae of the rough endoplasmic reticulum. This finding suggests intracellular storage possibly reflecting a defective intracellular transport of fibrinogen.

Heterozygous PMS2 germline mutations are associated with Lynch syndrome. Up to one third of these mutations are genomic deletions. Their detection is complicated by a pseudogene (PMS2CL), which – owing to extensive interparalog sequence exchange – closely resembles PMS2 downstream of exon 12. A recently redesigned multiplex ligation-dependent probe amplification (MLPA) assay identifies PMS2 copy number alterations with improved reliability when used with reference DNAs containing equal numbers of PMS2- and PMS2CL-specific sequences. We selected eight such reference samples – all publicly available – and used them with this assay to study 13 patients with PMS2-defective colorectal tumors. Three presented deleterious alterations: an Alu-mediated exon deletion; a 125-kb deletion encompassing PMS2 and four additional genes (two with tumor-suppressing functions); and a novel deleterious hybrid PMS2 allele produced by recombination with crossover between PMS2 and PMS2CL, with the breakpoint in intron 10 (the most 5′ breakpoint of its kind reported thus far). We discuss mechanisms that might generate this allele in different chromosomal configurations (and their diagnostic implications) and describe an allele-specific PCR assay that facilitates its detection. Our data indicate that the redesigned PMS2 MLPA assay is a valid first-line option. In our series, it identified roughly a quarter of all PMS2 mutations. © 2012 Wiley Periodicals, Inc.

References1 , Chan JKC, Carcangiu ML. Rosai J. Papillary carcinoma of thyroid with exuberant nodular fasciitis-like stroma. Report of three cases. Am. J. Clin. Pathol. 1991; 95; 309-314. 2. Carcangiu ML, Zampi G, Rosai J. Papillary thyroid carcinoma: a study of its many morphological expressions and clinical correlates. Pathol. Annu. 1985: 20; 1-44. 3. Chan JKC. Saw D. The grooved nucleus. A useful diagnostic criterion of papillary carcinoma of the thyroid. Am. J. Surg. Pathol. 1986; 1 0 672-679.Figure 3. Case 1. Metastatic foci of papillary carcinoma in lymph node devoid of fasciitis-like stroma.

Our study showed that MSI is not implicated in the pathogenesis of a subset of HCC affecting elderly patients without chronic liver disease. Further studies are needed to clarify the pathogenesis of HCC in this particular setting.