The human hematopoietic progenitor cell antigen CD34 is synthesized and expressed by early normal hematopoietic progenitor cells and by many acute leukemias. Anti-CD34 antibodies also have been reported to stain blood vessels in tissue sections, and, more recently, CD34 mRNA has been detected in vascular endothelial cells. Therefore, the authors studied the diagnostic utility of immunohistochemical CD34 antigen detection in tumors of endothelial cell derivation and compared the results with stains for von Willebrand (vW) factor. A wide variety of epithelial and mesenchymal neoplasms also were examined to assess the specificity of CD34 for vascular neoplasia. Seven cases of angiosarcoma (seven of seven), five cases of Kaposi's sarcoma (five of five), and eight cases of epithelioid hemangioendothelioma (eight of eight) were moderately to strongly positive for CD34. This reactivity was equally intense in frozen sections, alcohol-fixed tissue, and formalin-fixed specimens. In many cases, the malignant endothelial cells stained more strongly than adjacent benign endothelium. Moreover, in most cases CD34 positivity was quantitatively and qualitatively stronger than staining for vW factor. Two cases of hemangiopericytoma (two of two) were CD34 positive but stained less intensely than the angiosarcomas, Kaposi's sarcomas, or hemangioendotheliomas. Five of six cases of hemangioma also stained positively for CD34; the nonreactive tumor in this group was the only one among 28 vascular neoplasms studied that was not reactive for CD34. In comparison, 9 of the 28 vascular tumors did not stain for vW factor. Three hundred fifty-seven tumors of nonvascular derivation also were examined for CD34 antigen expression. Focal light staining was seen in one pulmonary squamous cell carcinoma; moderate to intense staining was observed in half of the epithelioid sarcomas studied (8 of 16) and in a minority of leiomyosarcomas (3 of 22). These findings indicate that CD34 is a sensitive and relatively specific marker for neoplasms of vascular origin.

Oncotype DX(TM) is an RT-PCR-based assay used to predict chemotherapy benefit in patients with estrogen receptor (ER) positive breast cancers. We were interested if routinely available pathologic parameters could predict Oncotype DX Recurrence Scores (RS) in subsets of patients. We identified 173 breast cancers with available RSs and used 104 of these as a test set and 69 cases as a validation set. Pathologic characteristics including size, histologic type, Nottingham grade, and lymphatic invasion were recorded. Test set cases were stained for ER, progesterone receptor (PR), HER2, Ki67, CyclinD1, BCL2, D2-40, and P53. Statistical correlations with RS and regression tree analysis were performed. The validation set was subjected to analysis on the basis of grade, PR, and Ki67. In the test set, grade, PR levels and Ki67 had the strongest correlation with RS (P = 0.0002-0.0007). Regression tree analysis showed grade and PR as factors that could segregate cases into RS categories, with Ki67 adding value in certain subsets. A subset of cancers with a high likelihood of having a low RS (0-18) was identified with the following characteristics: grade 1, strong PR expression (Allred score ≥ 5) and Ki67 ≤ 10%. No cases with these characteristics had a high RS (≥ 31) and 73% had a low RS. Cancers highly likely to have a high RS were grade 3, low to absent PR expression (Allred score <5) and Ki67 > 10%. 80% of cases with these characteristics had a high RS and no cases had a low RS. Our validation set had similar findings in these two subsets. In conclusion, When cost and time are a consideration and the added value of Oncotype DX(TM) testing is in question, it may be reasonable to assume the results of this test in two specific subsets of breast cancers: (1) grade 1, high PR, low Ki67 cancers (low RS), and (2) grade 3, low PR, high Ki67 cancers (high RS).

Context.-Identification of the site of origin of carcinoma of unknown primary using immunohistochemistry is a frequent requirement of anatomic pathologists. Diagnostic accuracy is crucial, particularly in the current era of targeted therapies and smaller sample sizes.Objectives.-To provide practical guidance and suggestions for classifying carcinoma of unknown primary using both proven and new antibodies, as well as targeting panels based on integration of morphologic and clinical features.Data Sources.-Literature review, the authors' practice experience, and authors' research.Conclusions.-With well-performed and interpreted immunohistochemistry panels, anatomic pathologists can successfully identify the site of origin of carcinoma of unknown primary. It is crucial to understand not only the diagnostic uses of the many available antibodies but also the potential limits and pitfalls.

Our results support the findings of recent pangenomic studies that true polysomy 17 is uncommon. Additional FISH studies that use probes to the SMS, RARA, and TP53 genes are an effective way to determine the true HER2 amplification status in patients with polysomy 17 and they have important potential implications for guiding HER2-targeted therapy in breast cancer.