Hematoxylin and eosin–stained, paraffin-embedded tissue sections from old C57Bl/6 Fancc^-/- mice. (A) Small intestine lymph node showing histiocytic sarcoma with sheets of neoplastic cells characterized by eosinophilic cytoplasm and pleomorphic nuclear morphology. (B) Mammary adenocarcinoma with well-circumscribed and encapsulated mass composed of neoplastic cells with oval or polyhedral nucleus with either amphophilic nuclei and stippling or coarse pattern to their chromatin. Anisokaryosis is 2-fold and mitotic index is 5. Original magnification × 100.