A staging system based on histopathologic evaluation of skin, lymph nodes, blood, and visceral sites provides more comprehensive prognostic information than clinical evaluation of skin disease and adenopathy. Patients may be divided at initial presentation into three prognostic groups: good-risk patients, who have plaque-only skin disease without lymph node, blood, or visceral involvement (median survival, greater than 12 years); intermediate-risk patients, who have cutaneous tumors, erythroderma, or plaque disease with node or blood involvement but no visceral disease or node effacement (median survival, 5 years); and poor-risk patients, who have visceral involvement or node effacement (median survival, 2.5 years).

Histiocytic sarcoma (HS) is an extremely rare non-Langerhans cell disorder with an aggressive course and limited treatment options. Recent advances in molecular/genetic sequencing have suggested a common clonal origin between various hematolymphoid disorders and cases of secondary HS. Deriving conclusions from previously reported cases of HS arising secondarily to certain hematolymphoid disorders, here we have tried to provide insight into the mechanisms influencing this evolution. We also discuss a clinical case of a 72-year-old man with a diagnosis of chronic myeloid leukemia (CML), presenting subsequently with a heterogeneous liver mass positive with a diagnosis of HS. The liver mass showed a retained BCR-ABL1 translocation suggesting clonality between the CML and HS. As seen in our case and other reported cases of HS derived secondarily, the concurrent expression of immunoglobulin heavy (IGH)-/lightchain rearrangements or cytogenetic markers common to the primary malignancy suggests an evolutionary mechanism involving lineage switching that could potentially be influenced by genetic or epigenetic cues which may occur at the level of a progenitor or the malignant cell itself. Clinical caseA 72-year-old male was brought to the emergency room with a one-month history of progressively worsening bilateral lower extremity swelling, more than 10 lbs. of weight loss, lack of appetite, and rapidly declining performance status. His past medical history was notable for CML, which was diagnosed 30 months prior to presentation (Fig. 1). The patient was treated on a protocol with imatinib (400 mg daily) and demonstrated a complete molecular response to tyrosine kinase inhibitor (TKI) therapy. Focused physical examination demonstrated an emaciated male in mild distress from abdominal pain, right upper quadrant tenderness on deep palpation, and abdominal distension without any signs of an acute abdomen.His peripheral blood smear revealed normochromic, normocytic anemia with hemoglobin of 7.6 g/dL (normal range, 12.5-16.3 g/dL), a white blood count of 7 730/lL (normal range, 3 600-11 200/lL), a red blood cell count of 2.78 M/lL (normal range 4.06-5.63 M/lL), and a platelet count of 114 000/lL (normal range, 159 000-386 000/lL). Serum iron was low (21 lg/dL) with a low TIBC (216 lg/dL), which was attributed to anemia of chronic disease. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed the absence of the BCR/ABL transcript in the peripheral blood.Computed tomography scan of the chest and abdomen revealed a large, complex, heterogeneous, hypodense mass involving nearly all of the caudate and left lobes of the liver. These lesions were not present in the previous examination carried out 1 year before.Biopsy of the liver mass revealed diffuse infiltration of large and irregular pleomorphic cells with lobulated nuclei with some binucleated and trinucleated cells containing

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