Haemophagocytic histiocytic sarcoma

The following are histopathology (H&E x400) sections from an enlarged spleen with multiple, poorly delineated nodules in an 8-year old Rottweiler that presented with regenerative anaemia.

Fig 1. The spleen is multifocally to extensively infiltrated by a neoplastic and pleomorphic round cell population. Neoplastic round cells frequently contain intracytoplasmic red blood cells consistent with erythrophagia (black arrows).
Fig 2. A large proportion of the neoplastic cells also display haemosiderin-accumulation characterised by intracytoplasmic brown granular pigment (green arrows) that indicates red blood cell breakdown. Occasional multinucleated cells are noted (black arrow).
Fig 3. Mitotic figures are relatively frequent (red arrow).

Final Diagnosis

Splenic haemophagocytic histiocytic sarcoma


Haemophagocytic histiocytic sarcoma (formerly known as malignant histiocytosis) is an uncommon malignant neoplasm in which the neoplastic histiocytes display erythrophagia and/or haemosiderin-accumulation resulting in progressive anaemia. The spleen is the most commonly affected organ but the liver, lungs, lymph nodes and bone marrow are also frequently involved. Generalised hepatosplenomegaly and lymphadenopathy are common clinical findings. Disease progression is typically rapid and unfortunately the prognosis is poor.