Objective: Myeloid sarcoma is a localized mass of myeloblasts or immature myeloid cells involving any extramedullary site. Reports in the literature documenting leukemic infiltration of appendix are uncommon and extremely rare when symptoms mimicking typhlitis. Method: A 30-year-old man with a history of relapsed acute myelogenous leukemia (FAB classification, M2) admitted for receiving induction chemotherapy. After 10 days of chemotherapy, he presented with fever, nausea, vomiting, abdominal pain and severe neutropenia (0.026×109/L as absolute neutrophil count). This manifestation was attributed to typhlitis and he received antibiotic therapy, but he came back 50 days later with acute abdomen prompting exploratory laparotomy which revealed inflamed appendix. Results: Histologic examination showed diffuse appendiceal wall infiltration of mononuclear cells with medium-to-large vesicular nuclei, conspicuous nucleoli and pale eosinophilic cytoplasm. Immunostains showed the diagnosis of granulocytic sarcoma with myeloperoxidase, leukocyte common antigen, CD15, CD117 and CD68 positivity and epithelial membrane antigen, keratin, CD3, CD5, CD10, CD79a and CD20 negativity. Conclusion: Our case declares that physicians and surgeons should be aware of granulocytic sarcoma in the differential diagnosis of mild tenderness on palpation of the abdomen as a complication of acute myelogenous leukemia. Objective: Angioimmunoblastic T-cell lymphoma (AITL), one of the most frequent entities among peripheral T-cell lymphoma, is characterized by lymphadenopathy, B-symptoms, and an aggressive behaviour. Method: We reported 3 cases of AITL during a period of 4 years (2004) (2005) (2006) (2007) . Results: The age of patients varied between 20 and 73 yearold. They hadn't any pathologic history. Two patients presented with a multiple cervical lymphadenopathy, and weight loss. The other patient had fever and sweat. Physical examination found multiple lymph nodes with hepatosplenomegaly in 2 patients. Abdominal ultrasound and CT-scan showed diffuse lymphadenopathy with features raising the possibility of lymphoma. The diagnosis of AITL was confirmed by a microscopic and an immunhistochemical study of lymph node or liver biopsy. 2 patients received a cure of chemotherapy Conclusion: Angioimmunoblastic T-cell lymphoma (AITL) is an aggressive non-Hodgkin T-cell lymphoma. AITL is frequently associated to immunological and hematologic diseases such as autoimmune hemolytic anemia, vasculitis, rheumatoid arthritis, and autoimmune thyroid disease. Its natural history has been the subject of controversy, considered for many years to be a nonmalignant disorder or a dysimmune disease, until the clonal nature of AITL was proven by molecular studies. Although patients are usually treated with corticosteroids, chemotherapy, and/or plasmapheresis, outcomes were dismal. Objective: Low grade lymphomas (indolent) are commonly located on extranodal sites. nodal location are relatively of low incidence. Our aim is to describe the epidemiological status of NBCL and to assess their pathological features in the center of Tunisia. Method: We report 50 cases of indolent NBCL diagnosed in the department of pathology, during a period of 10 years (2000-2009) . Clinical, pathological and immunohistochemical (large panel of antibodies), treatment and outcome data are collected. Results: The mean age was 63 year old (33 and 89 years). The sex ratio was 1.27. NBCL was 6.5 % of all N H lymphomas and 42.73 % of indolent NBCL of any sites. Nodal enlargement and hepatomegaly were the main symptoms. Small Lymphocytic lymphomas were the most frequent variant (56 %), followed by follicular lymphomas (26 %). Mantle cell lymphoma and marginal zone B cell lymphoma were rare (12 % and 6 %, respectively). They were exclusively of B cell type. 76 % of cases were in stage III-IV. 90 % of patients received chemotherapy. 2 % of recurrence and 48 % of death were found. Conclusion: NBCL in the center of Tunisia are relatively uncommon. Small lymphocytic lymphoma is the most frequent in our population. They are still of relatively worse prognosis. Objective: Bone marrow metastases can be found in some malignant tumors, but diagnosing a nonhematologic malignancy from marrow is an unusual event. Herein we present a case of metastatic signet ring cell carcinoma with an unknown primary site. Method: A 39 year-old woman admitted to the Hospital with weakness and bone pain. Positron emission tomography/computed tomography (PET/CT) revealed disseminated bone lesions showing increased metabolic activity. Bone marrow biopsy and aspiration were performed. Results: Bone marrow biopsy revealed extensive necrosis and nearly total replacement of normal bone marrow elements by atypical tumoral cells. Tumoral cells were arranged individually or in small clusters, having hyperchromatic, eccentric located nuclei and abundant cytoplasm with signet ring cell morphology. Even after thourough investigation of all the systems, a primary site of malignancy could not be detected. She received nine cycles of chemotherapy. Craial MRI revealed multiple metastatic lesions. 9 months after the initial diagnosis, she died of disseminated metastatic lesions. Conclusion: Even after thorough investigations, a primary site of malignancy could not be detected. In the literature, all the presented cases had very short survival varying from days to a few months. Our patient lived for 9 months with multidiciplinary approach. Objective: Approximately 20 % of follicular lymphomas (FLs) are bcl2 negative and 10-15 % of FLs lack a translocation t(14;18). Previously we have found that negative bcl2 staining in cases that do have a t(14;18) is caused by mutations in the epitope for the bcl-2 antibody, but this is never the case in bcl-2 negative, t (14;18) negative cases. Now that translocation detection is more commonly performed we noticed that many of the cases that were referred to us as translocation negative FL are actually often nodal marginal zone lymphomas (NMZLs) with extensive follicular colonization. Method: t(14;18) negative cases that on H&E sections look like FL were analyzed by morphology and immunohistochemistry, including antibodies against CD10, bcl-2, Ki-67, and CD23. Results: Careful observation of the bcl-2 staining pattern revealed that follicles that appeared positive at low power contained negative cells at high magnification. The amount of negative cells varied from follicle to follicle and was associated with the extent of Ki-67 positivity. Conclusion: Based on morphology and immunohistochemistry we reclassified many cases of bcl-2 positive, t(14;18) negative FL into NMZL. Although there is presently no positive marker for NMZL, we believe that such cases are responsible for most t(14;18) negative FL. Objective: Recent studies do not provide a definite answer on the origin and pathogenesis of lichen planus (LP). Histologic findings are the same, regardless of the area involved. Electron microscopy is useful to confirm the diagnosis in atypical cases and monitoring LP development. This study aimed an ultrastructural characterization of keratinocyte degeneration in pemphigoides, hypertrophic, and follicular LP types correlating this with levels of gelatinolytic activity caused by metalloproteinase-9 (MMP-9).