EAHP 2020 workshop proceedings, pediatric myeloid neoplasms.

The first section of the bone marrow workshop of the European Association of Haematopathology (EAHP) 2020 Virtual Meeting was dedicated to pediatric myeloid neoplasms. The section covered the whole spectrum of myeloid neoplasms, including myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), myelodysplastic/myeloproliferative neoplasms (MDS/MPN), and acute myeloid leukemia (AML). The workshop cases are hereby presented, preceded by an introduction on these overall rare diseases in this age group. Very rare entities such as primary myelofibrosis, pediatric MDS with fibrosis, and MDS/MPN with JMML-like features and t(4;17)(q12;q21); FIP1L1::RARA fusion, are described in more detail.

Myelodysplastic/myeloproliferative neoplasms: are morphology and immunophenotyping still relevant?

The term myelodysplastic/myeloproliferative neoplasm (MDS/MPN) refers to a group of clonal hematopoietic neoplasms with overlapping clinical, morphologic and genetic myelodysplastic and myeloproliferative features observed at the time of first presentation. Impaired hematopoiesis morphologically associated with evidence of myelodysplasia manifests clinically with cytopenia/s. Simultaneously, myeloproliferation is seen within the bone marrow and leads to cytosis in the peripheral blood. The diagnostic category of MDS/MPN encompasses a heterogeneous group of diseases which share similarities among them, but at the same time have distinct clinical and pathologic features and eventually diverse prognosis; such differences justify their separation in a classification scheme. In the era of genetic and genomic tests, their distinction from conventional myelodysplastic syndromes or myeloproliferative neoplasms still relies on close clinocopathological correlation, with evaluation of both peripheral blood and bone marrow samples being essential in this sense. A multiparametric integration of clinicopathologic data and cytogenetics and molecular genetics results is the preferred diagnostic approach.

The clinicopathologic significance of lymphocyte subsets in acute myeloid leukemia.

INTRODUCTION: While the role of the immune system in altering and modulating the progression of solid tumors is well studied, the impact of the immune system on the outcome and progression of hematolymphoid neoplasms is still poorly understood. METHODS: Here, we report a retrospective study detailing our analysis of 130 patients with acute myeloid leukemia (AML), with flow cytometry immunophenotypic evaluation of major lymphocyte subsets including B cells, T cells, and NK cells. RESULTS: Our study identifies differential signatures of lymphocyte subsets pertaining to distinct subcategories of AML, and prognostic correlations in patients. In multivariate analysis, NK cells (specifically CD56+/CD16+ NK cells at a cutoff of ≥5%) were found to be an independent indicator of improved overall and disease-free survival; cytogenetic risk was also shown to be critical in stratifying patients with AML. CONCLUSIONS: In total, we demonstrate that in AML, the subset distribution of immune system lymphocytes is nonrandom, and suggest an important role for distinct lymphocyte subsets, particularly NK cells, in this disease.

A study of disseminated intravascular coagulation in acute leukemia reveals markedly elevated D-dimer levels are a sensitive indicator of acute promyelocytic leukemia.

INTRODUCTION: While the presence of disseminated intravascular coagulation (DIC) has been implicated in worse clinical outcome in acute leukemia, the relationship between different subtypes of acute leukemia and the clinicopathologic features of DIC has not been systematically well studied. METHODS: In this study, we retrospectively reviewed 149 cases of newly diagnosed acute leukemia and assessed the utility of evaluating red blood cell morphologic features, and coagulation parameters in determining the presence of DIC as well as differentiating subtypes of acute leukemia. RESULTS: Review of our cohort demonstrates a novel finding, that elevated D-dimer concentrations ≥19 000 ng/mL fibrinogen equivalent units (FEU) are a sensitive diagnostic indicator of acute promyelocytic leukemia (APL) with moderate specificity, sensitivity 96%, specificity 92% in acute leukemia subtyping. Similar to other studies, APL showed an increased incidence of DIC (P < 0.01) compared to other subtypes of acute leukemia. Surprisingly, the presence of schistocytes on the peripheral blood smear was not a statistically significant indicator of DIC, sensitivity of 36% and specificity of 89%. Finally, the presence of DIC was not a significant indicator of poorer prognosis amongst all patients with AML. CONCLUSION: Overall we identify elevated D-dimer concentrations ≥19 000 ng/mL FEU are a sensitive indicator of acute promyelocytic leukemia (APL), with a sensitivity of 96% and specificity of 92% in the subtyping of acute leukemias, and that the presence of schistocytes in peripheral blood smears is not a diagnostically sensitive screening test for DIC with a sensitivity of 36%.

High frequency of pro-B acute lymphoblastic leukemia in adults with secondary leukemia with 11q23 abnormalities.

To evaluate the frequency and cytogenetic and immunophenotypic features of therapy-related, precursor B-cell acute lymphoblastic leukemia (ALL), 152 cases of immature B-cell ALL were reviewed. These were compared to the frequency of therapy-related acute myeloid leukemia (t-AML) during the same time period. Eight ALL cases with a prior diagnosis of malignancy were identified, including six (4.0%) with prior therapy considered to be therapy-related ALL (t-ALL). The t-ALL cases followed treatment for breast carcinoma (two cases), lung carcinoma (two cases), lymphocyte predominance Hodgkin's disease and follicular lymphoma with a latency period of 13 months to 8 years. All t-ALL cases had a pro-B (CD10-negative) immunophenotype with significantly higher expression of CD15 and CD65, compared to the de novo CD10-positive ALL cases. All six t-ALL cases had MLL abnormalities by fluorescence in situ hybridization, and four showed t(4;11)(q21;q23). These represented half of all 11q23-positive adult ALL cases. During the same time period, 4.9% of all AML cases were considered t-AML. There was a 16.7% frequency of 11q23 abnormalities in the t-AML group. Despite the similar frequency in therapy-related disease among ALL and AML cases, there were differences in the frequency of the diseases and t-ALL represented 12% of all therapy-related leukemias. However, t-ALL represented 46% of all 11q23-positive therapy-related leukemias. The immunogenetic features of t-ALL appear distinct and may aid in identifying more cases of this disease type in the future.

Primary myelodysplasia occurring in adults under 50 years old: a clinicopathologic study of 52 patients.

Although myelodysplastic syndromes (MDSs) are generally thought to be diseases of elderly patients, younger patients also have rarely been diagnosed with MDS. This is a report of the clinical, morphologic and cytogenetic features of 52 cases of primary MDS occurring in adults under the age of 50 years. Cases secondary to chemotherapy or radiotherapy were excluded. There were 31 males and 21 females. The median age at presentation was 39 years (range, 18 to 49 years). The interval between onset of symptoms and diagnosis was brief (median, 4 weeks; range, 1-32 weeks). Of the 49 patients for whom information about duration of symptoms was available, 13 (27%) were asymptomatic. Forty-two (81%) of the patients were classified using FAB criteria for blood and bone marrow morphology: refractory anemia (RA), 11; refractory anemia with ringed sideroblasts (RARS), four; refractory anemia with excess blasts (RAEB), 12; chronic myelomonocytic leukemia (CMML), three; refractory anemia with excess blasts in transformation (RAEB-T), 12 patients. Ten patients could not be categorized. Abnormalities involving chromosome 7 was the most frequent cytogenetic abnormality (31%). Partial chromosomal deletion and chromosome gain were also common abnormalities (22% and 9%, respectively). Translocations accounted for only 9% of the main cytogenetic abnormalities encountered in this patient population. For the 49 patients for whom information regarding AML transformation was available, 23 (47%) progressed to acute myeloid leukemia, with an overall median time to progression of 2 months (range 3 weeks to 3 years). In each category except for RARS, approximately half of the patients progressed, with a slightly less median time to progression in RAEB-T than for the other subtypes of MDS. Thirteen patients underwent bone marrow transplantation at the time of presentation of their disease.

Toward the validation of aneusomy detection by fluorescence in situ hybridization in bladder cancer: comparative analysis with cytology, cytogenetics, and clinical features predicts recurrence and defines clinical testing limitations.

Fluorescence in situ hybridization (FISH) is regarded as a potential new tool for the clinical management of bladder cancer that works by detecting cytogenetic aberrations in noncycling, exfoliated cells from bladder irrigations. However, clinical validation steps must be addressed to define the true predictive potential in a clinical setting. Toward the validation of FISH with the use of bladder washings and prior to incorporation into a large, prospective clinical trial, a pilot study was designed to determine its clinical potential, define testing limitations, optimize a panel of probes specific for bladder cancer detection, and outline protocol/data collection parameters. Correlations with standard cytogenetics and clinicopathological features of bladder cancer were investigated. Exfoliated cells obtained from benign bladder washings served as normal controls. The results of this pilot study suggest the following: (a) FISH and cytology are complementary testing procedures; however, the FISH data provided valuable ploidy and specific genotypic information for recurrent tumors in "suspicious" cases; (b) chromosomal aberrations defined by FISH are associated with tumor grade and stage (i.e., simple numerical aberrations were associated with low-grade tumors, and high-grade and invasive tumors exhibited multiple, nonrandom chromosomal aberrations and vast intratumor heterogeneity); (c) somatic pairing or homologous centromeric association can give a false-positive result and appears to be linked to prior therapy; (d) dual hybridization with reference gene-specific probes must be used to control for somatic pairing; and (e) focal, deep muscle invasive lesions, with no surface exposure, may yield false-negative results. The data suggest that FISH analysis, with the use of cells isolated from bladder washings, is a powerful technique holding promise for early cancer detection, monitoring treatment outcome, and predicting recurrence of disease.

The diagnostic and clinical impact of genetics and epigenetics in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a complex disease, for which our understanding of the role of genetic and epigenetic changes has undergone significant advancements. Newer diagnostic and prognostic classifications have increasingly incorporated such information, and novel therapies have been developed to target specific genes, processes, and pathways based on this growing understanding. Given the rapid evolution of this field, it is critical for physicians and translational researchers to have a more in-depth understanding of this evolving landscape. Here, we review both genetics and epigenetics in acute myeloid leukemia from a practical standpoint.

Evaluation of T cell receptor testing in lymphoid neoplasms: results of a multicenter study of 29 extracted DNA and paraffin-embedded samples.

To evaluate current diagnostic methods used for the evaluation of T cell receptor (TCR) gene rearrangements, 24 different laboratories analyzed 29 lymphoid neoplasm samples of extracted DNA and paraffin-embedded tissue and were asked to complete a technical questionnaire related to the testing. Participating laboratories performed Southern blot and polymerase chain reaction (PCR) testing for rearrangements of the TCRbeta chain gene and PCR for the TCRgamma chain gene rearrangements. Of 14 laboratories performing TCRbeta Southern blot analysis, there was complete agreement in 10 of 14 cases, with some false negative results obtained in 4 cases. No false positive results were obtained by Southern blot analysis. TCRbeta PCR analysis was only performed by two laboratories, and only 47.1% of positive samples were detected. Twenty-one laboratory results were obtained for TCRgamma PCR. This method showed an overall detection rate of 77.9% for T cell gene rearrangements with a 4.1% false positive rate, as compared to both TCRgamma Southern blot analysis results and immunophenotyping. The detection rate for TCRgamma PCR, however, significantly differed when extracted DNA samples from frozen tissue were compared to paraffin-embedded tissue (85.4% versus 65.9%; P = 0.0005). Significant differences in true positive results were obtained when laboratories using primers directed against multiple TCRgamma variable regions (V1-8 plus one to three other primer sets) were compared to laboratories that used only a single set of TCR primers directed against the V1-8 (P < 0.0001). Other technical factors significantly affecting results were also identified. These findings provide useful data on the current state of diagnostic TCR testing, highlight the risk of false negative results for TCR testing directed against only portions of the TCRgamma gene, and identify limitations of testing of paraffin-embedded tissues in some laboratories.

Vimentin-negative epithelioid sarcoma. The value of an immunohistochemical panel that includes CD34.

Virtually all reported cases of epithelioid sarcoma have been vimentin rich, and the coexpression of vimentin and keratin is considered a characteristic immunophenotype in these tumors. We report three cases of soft tissue tumors with histologic and clinical features consistent with epithelioid sarcoma, all of which failed to immunoreact by standard immunohistochemistry for vimentin using two different monoclonal antibodies. Antigen retrieval demonstrated focal vimentin staining in one case, whereas the other two remained negative. An extensive panel of immunohistochemical stains revealed strong diffuse staining with keratin and epithelial membrane antigen in all three cases as well as patchy membrane staining with an antibody to CD34. CD34 positivity is commonly seen in epithelioid sarcoma, but it is very rarely found in carcinomas. We conclude that these cases represent a unique immunophenotypic variant of epithelioid sarcoma that can be immunohistochemically confirmed, despite the lack of identifiable vimentin, by their immunoreactivity for keratin and CD34.

Splenic mesothelial cysts mimicking lymphagiomas.

Lymphangiomas of the spleen may occur as part of lymphangiomatosis or may represent solitary lesions. Solitary splenic lymphangiomas are described traditionally as subcapsular, multicystic proliferations that are often incidental findings. Six cases of splenic tumors with morphologic features similar to those described for solitary lymphangioma were studied using an immunohistochemical panel that included epithelial and vascular markers. None of the patients had evidence of lymphangiomatosis, and all tumors were incidental findings in splenectomy specimens. All cases demonstrated lining cells that were positive for keratin and the mesothelial cell-associated antibody HBME-1 but were negative for the vascular markers Factor VIII-related antigens, CD31, and CD34. The immunohistochemical findings are suggestive of a mesothelial derivation of these multicystic proliferations rather than representing true lymphangiomas.

Large solitary fibrous tumor of the kidney: report of two cases and review of the literature.

Solitary fibrous tumors are spindle cell neoplasms frequently arising in the serosal surface as well as a variety of other sites. We report two cases of large solitary fibrous tumor arising in the kidney, clinically thought to be renal cell carcinoma, in 41- and 72-year-old men. Although large in size (13.0 and 14.0 cm in greatest dimension, respectively), both lesions were well circumscribed and composed of a mixture of spindle cells and dense collagenous bands with no areas of necrosis or cystic changes noted macroscopically or microscopically. Immunohistochemical studies revealed reactivity for vimentin, CD34, collagen IV, and bcl-2 protein in both cases, with no staining for keratin, S-100 protein, or muscle markers, confirming the diagnosis of solitary fibrous tumor of the kidney. Solitary fibrous tumor of the kidney is rare but may present as a large mass that may be clinically confused with carcinoma or sarcoma.

Non-Hodgkin's lymphoma involving the breast.

Breast involvement by non-Hodgkin's lymphoma is rare. Differences between primary and secondary breast lymphoma have been reported, and a relationship between primary breast lymphoma and lymphomas of mucosa-associated lymphoid tissue has been suggested. We reviewed 61 cases of breast lymphoma (41 primary, 13 secondary, and 7 unclear) that included 28 right-sided masses at presentation, 17 left-sided, 12 bilateral, and 4 in which the side was not known. A subgroup of bilateral breast lymphomas was identified that occurred in young women, four of which were pregnant or postpartum. A high incidence of intermediate- and high-grade lymphomas were present in both cases of primary and secondary lymphomas as was a high frequency of B-cell phenotype. Additional immunohistochemical studies failed to demonstrate evidence of marginal or mantle cell differentiation in seven of eight cases studied. Lymphoepithelial lesions were identified in a majority of cases, including 67% of primary and 64% of secondary lymphomas. This study failed to demonstrate a morphologic difference between primary or secondary lymphomas of the breast and suggests that breast lymphomas differ from other extranodal lymphomas in that the latter are frequently low grade.

Peripheral T-cell lymphoma with Toutonlike tumor giant cells associated with HIV infection: report of two cases.

T-cell lymphoma in patients infected with HIV is much less common than B-cell lymphoma. We describe two cases of HIV-associated extranodal lymphoma that showed Toutonlike tumor giant cells and mononuclear large lymphoma cells. Both cell types expressed T-cell-associated antigens, including CD3, CD5, CD43, and CD45RO, and were CD4- and CD30-positive and negative for all B-lineage-associated antigens. Both cases showed T-cell receptor gamma chain gene rearrangements using the polymerase chain reaction and were negative for the Epstein-Barr virus by in situ hybridization. Despite the expression of CD30 by the multinucleated cells, both cases were negative for ALK1 by immunohistochemistry and failed to show evidence of the nucleophosmin-anaplastic lymphoma kinase fusion product characteristic of t(2;5) using the reverse-transcriptase polymerase chain reaction. Although rare, CD4-positive, T-cell lymphoma with Toutonlike giant cells may be a distinct type of HIV-associated malignant lymphoma.

Sinonasal NK/T-cell lymphomas in the United States.

Sinonasal natural killer (NK)/T-cell lymphomas are common in Asia and areas of South and Central America but are rarely seen in the United States, where they have not been as well characterized. Fifteen cases diagnosed in Southern California were studied with respect to histologic features, immunophenotype, Epstein-Barr virus EBER in-situ hybridization (EBV EBER-ISH), and T-cell receptor gamma chain (TCR-gamma) gene rearrangement. Although ethnic background was available for only seven patients, six were of Asian or Hispanic descent with only one non-Hispanic white known. Twelve presented as sinonasal lesions, but three were limited to the oropharynx. Most cases (11 of 15) demonstrated both necrosis and an angiodestructive pattern. All cases demonstrated cytoplasmic CD3 positivity (15 of 15), and were positive for both TIA-1 and granzyme B (14 of 14). Perforin was positive in 5 of 14. CD56 was expressed in 10 of 15 and CD8 in 3 of 15. EBV EBER-ISH was positive in 14 of 14 and TCR-gamma gene rearrangement was detected in 1 of 14 cases. None (0 of 14) were positive for CD16 or CD57. Although CD16-positive histiocytes were abundant, double-label EBER-ISH/IHC failed to identify CD16 expression on EBV-positive tumor cells. Three cases with pleomorphic large cell morphology showed focal CD30 positivity, raising the differential diagnosis of anaplastic large cell lymphoma, but all were ALK-1-negative and otherwise similar to the other cases of NK/T-cell lymphoma. Sinonasal NK/T-cell lymphomas in the United States most often occur in ethnic groups from areas of reported high frequency (Asia, Central and South America), although less commonly than in endemic populations, and are otherwise similar phenotypically. A combined approach, including immunohistochemistry, EBV EBER-ISH, and TCR gene rearrangement studies, is most helpful to arrive at the correct diagnosis.

Extramedullary myeloid cell tumors. An immunohistochemical and morphologic study of 28 cases.

In an attempt to correlate the morphologic and immunophenotypic findings in extramedullary myeloid cell tumors (EMT), we studied 28 cases with a large panel of antibodies using paraffin section immunohistochemistry. A previous or concurrent diagnosis of acute myelogenous leukemia or chronic myelogenous leukemia was made in 25 cases. Six EMT were morphologically classified as well differentiated (WD-EMT), 17 as poorly differentiated (PD-EMT), and five as blastic EMT. The WD-EMT were easily recognized morphologically and displayed a relatively mature myeloid phenotype, with elastase, CD15, and CD68 positivity in all cases. On the other hand, the five blastic-EMT displayed no morphologic evidence of myeloid derivation, were completely negative for CD15, and were weakly positive for elastase in only one case. The PD-EMT, with a morphologic appearance that resembles large cell non-Hodgkin's lymphoma, variably expressed CD15 and elastase. CD68 and lysozyme were present in the majority of PD-EMT, with some variability, but were negative in most blastic-EMT. CD45 (LCA) was detected in 75% of all EMT and CD34 was positive in 36%; neither antigen was significantly associated with a specific morphology. CD30 reactivity was not evident in any case, but slight positive staining was seen with CD20 (L26) in one WD-EMT. CD43 (Leu 22) was the only antibody that was positive in 100% of cases; staining was always intense and widespread. Antimyeloperoxidase (MPO) was positive in all cases but two, both with a blastic morphology. We conclude that (a) an immunohistochemical panel including CD20, CD43, CD68, and MPO can successfully identify the vast majority (96%) of EMT in paraffin sections, and (b) there is an association between morphology and phenotype in these lesions.

Splenic vascular tumors: a histologic, immunophenotypic, and virologic study.

Vascular tumors of the spleen include several different entities, some of which are unique to that organ. Twenty-two such proliferations were studied, including 10 hemangiomas, six littoral cell angiomas, four angiosarcomas, and two hamartomas. The hemangiomas included seven with localized tumors and three with diffuse angiomatosis of the spleen. All cases were studied by paraffin section immunohistochemistry with a large panel of antibodies. In addition, all cases were studied for the presence of the Kaposi's sarcoma-associated herpesvirus (KSHV) using the polymerase chain reaction. The morphologic findings were similar to those previously reported. All proliferations were vimentin positive, and one angiosarcoma was focally keratin positive. All cases reacted for CD31, whereas 20 of 22 were positive for von Willebrand's factor and 19 of 22 were positive for Ulex europeaus. CD34 expression in lining cells was identified in 10 of 10 hemangiomas, two of four angiosarcomas, and one of two hamartomas, whereas all six cases of littoral cell angioma were negative. CD68 was expressed in all cases of littoral cell angioma but was also positive in all three diffuse hemangiomas, two of seven localized hemangiomas, and two of four angiosarcomas. CD21 expression was restricted to the lining cells of littoral cell angioma, and CD8 expression was only identified in two of two hamartomas and two of four angiosarcomas. KSHV was not detected in any of the cases. These findings suggest that there are distinct immunophenotypic as well as morphologic features of splenic vascular tumors. Littoral cell angiomas have a characteristic CD34-/CD68+/CD21+/CD8- immunophenotype and hamartomas have a characteristic CD68-/CD21-/CD8+ phenotype. The frequent CD68 expression in diffuse hemangioma suggests an immunophenotypic difference from localized hemangioma of the spleen.

Follicular small lymphocytic lymphoma.

We herein provide evidence for the existence of a distinct morphologic form of small lymphocytic lymphoma (SLL) that we term follicular small lymphocytic lymphoma (FSLL). Nine specimens of FSLL from eight patients were studied. The lymphomas in this study showed a true follicular pattern that was independent of tissue planes; the cytologic composition was identical to that seen in SLL. All six of the specimens (from five patients) for which paraffin tissue was available marked as B cell phenotype and were positive for bcl-2 protein. Polymerase chain reaction studies performed on deparaffinized tissue sections showed bcl-2 major breakpoint region rearrangements in four of five cases for which study tissue was available. Clinical information was available for all eight patients. All patients presented with lymph node disease, and three patients also had extranodal involvement at the time of presentation. Three of the patients had a relapse of disease after 33-95 months, and two of these patients died soon after relapse. Another two of the eight patients never responded to chemotherapy and died of their disease after 2 and 8 months, respectively. Two patients died of causes unrelated to their lymphoma and unrelated to any lymphoma therapy. Only one patient remains disease-free, after 65 months; this patient had a relapse at 44 months. The finding of bcl-2 rearrangements suggests that the pathogenesis of FSLL is more closely related to follicular small cleaved cell lymphoma than to classic SLL.

Pathologic features of nodular lymphocyte predominance Hodgkin's disease in extranodal sites.

We describe the gross and histologic features of nodular lymphocyte predominance Hodgkin's disease (NLPHD) occurring in extranodal sites. Fifty-one specimens of NLPHD from 16 patients were studied. The sites of involvement were the spleen, liver, tonsil, salivary glands, skin, colon, soft tissue, and bone marrow, and the morphologic features were similar to those described in node-based NLPHD, including characteristic lymphocytic and/or histiocytic (L&H) cells that were easily identified in a background of a nodular proliferation of small lymphocytes and histiocytes. In the spleen, the normal architecture was generally preserved, and the tumor was found predominantly in the white pulp; the red pulp was rarely involved. In the liver, the tumor involved both the portal and parenchymal areas. In the tonsil, the lympohproliferation closely resembled the typical appearance of NLPHD in a lymph node. In all specimens with materials available for immunohistochemical studies, there were demonstrable L&H cells with an immunophenotype similar to node-based NLPHD, that is, CD45-positive, CD20-positive, and CD15-negative. The unique morphologic and immunologic characteristics of NLPHD are preserved in extranodal sites and allow its distinction from classic Hodgkin's disease and other lymphoproliferative malignancies that may occur in extranodal sites.

Keratin immunohistochemistry detects clinically significant metastases in bone marrow biopsy specimens in women with lobular breast carcinoma.

Some patients with breast cancer currently undergo bone marrow biopsy to make clinical decisions regarding therapy; however, lobular carcinoma can be difficult to detect in routine histologic sections. The authors reviewed retrospectively all available bone marrow biopsies from patients with lobular carcinoma diagnosed between January, 1, 1989, and September, 25, 1997, at the City of Hope National Medical Center to identify useful morphologic features and to determine the utility of pan-keratin immunohistochemical (IHC) staining. A total of 65 biopsies from 54 patients were reviewed. Thirteen of the 65 biopsies were classified initially as containing metastatic tumor based on histologic features alone. With the addition of keratin IHC, seven additional cases of metastatic disease were detected. Forty of the 54 patients received stem cell replacement or autologous bone marrow transplantation. Disease-free survival after high-dose chemotherapy with stem cell replacement or autologous bone marrow transplantation was stratified into three groups based on hematoxylin and eosin (H&E) staining and IHC results. Two-year disease-free survival was 33% for the H&E-/IHC+ group versus 90% for the H&E-/IHC- group (p = 0.005) among patients clinically free of disease at the time of stem cell replacement or autologous bone marrow transplantation. Two-year disease-free survival was 0% in the H&E+/IHC+ group (p = 0.04, compared with the H&E-/ IHC+ group). The authors conclude that routine morphologic examination without the aid of keratin IHC is unreliable in detecting clinically relevant metastatic lobular carcinoma in bone marrow biopsies. These findings suggest that pan-keratin immunostaining may be indicated on bone marrow biopsy specimens from lobular carcinoma patients if the biopsy appears histologically negative for metastatic tumor on H&E sections.