The Utility of Phosphohistone H3 (PHH3) in Follicular Lymphoma Grading: A Comparative Study With Ki-67 and H&E Mitotic Count.

OBJECTIVES: To determine the utility of phosphohistone H3 (PHH3) mitotic count (MC) in grading follicular lymphoma (FL). METHODS: FL cases were identified (2005-2017). Three hematopathologists recorded their average Ki-67 proliferation index, MC/high-power field (hpf) using PHH3 and H&E stains, and number of centroblasts/hpf. Results were assessed for correlations and interobserver variability. RESULTS: Forty-three cases of FL were studied. PHH3 MC resulted in the strongest correlation to grade (r = 0.701, P < .0001) compared with Ki-67 proliferation index (PI) (r = 0.681, P < .0001) and H&E MC (r = 0.536, P = .0002) and the strongest linear relationship to centroblast count (R2 = 0.453). Agreement among pathologists was strongest for PHH3 (intraclass correlation coefficient [ICC] = 0.86) followed by Ki-67 PI (ICC = 0.85) and H&E MC (ICC = 0.78). CONCLUSIONS: PHH3 correlates best to histologic grade and has less interobserver variability compared with Ki-67 PI and H&E MC. These results support using PHH3 as an adjunct in FL grading.

Aleukemic Myeloid Leukemia Cutis with a Kikuchi Disease-Like Inflammatory Pattern in Myelodysplastic Syndrome.

Myeloid leukemia cutis (MLC) is a rare disease characterized by the infiltration of neoplastic myeloid, myelomonocytic, or monocytic precursors into the skin, producing clinically nonspecific-appearing papules, nodules, plaques, or purpura that necessitate biopsy for definitive diagnosis. In general, it is considered an extramedullary manifestation of acute myeloid leukemia (AML) similar to myeloid sarcoma, also known as a chloroma. MLC often develops in patients with an established diagnosis of AML and is only rarely seen before the onset of systemic disease. Even more rarely, some patients are found to have an underlying nonleukemic bone marrow disease, such as a myelodysplastic syndrome (MDS). It is in these latter settings that the somewhat perplexing terminology aleukemic leukemia cutis (ALC) has been used widely. As may be imagined, establishing a diagnosis of ALC can be problematic and typically requires a high index of suspicion with careful integration of clinical, histopathological, and laboratory data. Once a diagnosis of ALC is made, a complete hematologic workup, including assessment of the patient's bone marrow, is essential because a diagnosis of MLC (with or without systemic leukemia) generally indicates a poor prognosis. When discovered in a patient with MDS, MLC has been suggested to herald progression toward more advanced disease. We present a rare case of so-called aleukemic myeloid leukemia cutis in an 82-year-old man subsequently diagnosed as having MDS without progression to overt AML. This case also illustrates a seemingly rare Kikuchi disease-like inflammatory pattern that obscured the underlying leukemic infiltrate in the skin, delaying its recognition.