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We reviewed 43 fine-needle aspiration biopsy (FNAB) smears with abundant extracellular mucinous material to determine whether accurate classification of mucinous lesions is achievable on FNAB: 26 had carcinoma (pure colloid carcinoma [CCA], 23; mixed CCA/invasive ductal carcinoma [IDC], 3); 17 had benign lesions on follow-up (benign MLL, 6; fibrocystic change [FCC], 6; myxoid fibroadenoma [MFA], 5). All carcinomas were identified correctly as malignant on FNAB. The initial cytologic diagnoses in benign cases were benign in 8, atypical in 8, and "suspicious" for carcinoma in 1. CCAs were moderate to markedly cellular with mild to moderate atypia and lacked oval bare nuclei. Marked nuclear atypia was confined predominantly to cases with mixed CCA/IDC. A distinct feature of CCA was thin-walled capillaries. FCCs and benign MLLs had overlapping cytologic features and showed variable cellularity and no or mild atypia. MFAs were markedly cellular with dyscohesion and variable atypia; stromal fragments and oval bare nuclei were present in every case. Mucinous lesions can be divided into 2 categories by FNAB: those that are adenocarcinomas and those that are not. CCAs have distinctive features that allow a definitive diagnosis on FNAB. Unnecessary surgery can be avoided in MFA by careful evaluation of smear characteristics. Cytologic features of FCC and MLL overlap. Owing to the documented association of MLL with carcinoma, we recommend that lesions that cannot be classified definitively as adenocarcinoma or MFA be considered for conservative excision, even in the absence of atypia.

Leukemic cells of bone marrow and peripheral blood showing clusters of distinctive, large, uniform, rounded intracytoplasmic inclusions were found in a patient who had acute lymphoblastic leukemia. These membrane-bound inclusions ranged from 0.8 to 1.4 microgram in diameter and were clearly demonstrated on routinely stained preparations. Electron microscopy disclosed transitions between well-developed mitochondria and the electron-dense structures. The functional significance of these presumably altered mitochondria is uncertain. Whorled lamellar internal structures, in occasional fingerprintlike arrangements, may represent duplication of mitochondrial cristae and, functionally, may reflect increased metabolic rate or otherwise abnormal metabolism. Cytochemical studies demonstrated the presence of both periodic acid-Schiff positivity and nonspecific esterase activity in these inclusions, but no peroxidase or acid phosphatase was found. These findings support the lymphoid nature of the disorder. Immunologic surface membrane markers are consistent with this case being, as with the majority of acute lymphoblastic leukemias, of non-B, non-T cell type. Cytogenetic studies on cultured leukemic cells from bone marrow and peripheral blood showed a consistently abnormal karyotype associated with the presence of an XXY chromosomal constitution. Since no other tissues (e.g., dermal fibroblasts) were examined, the diagnosis of Klinefelter's syndrome cannot be confirmed. A causal relationship between the coexistence of the abnormal karyotype and the acute leukemia was not proven but was suspected.