A Pain in the Butt: Marginal Zone Lymphoma of the Gluteus Muscle
Authors: Gamboa Eric O. , Pokuri Venkata , Batra Rashmi , Varma Mala 
Published: October 2019

Abstract
Abstract 5104
A 75-year-old man first noted a slowly enlarging left buttock mass about one year prior to his presentation to the hematology/oncology clinic. At that time, he was evaluated at the surgical clinic and imaging studies as well as a biopsy were recommended. The patient refused and was lost to follow-up. On presentation to the hematology/oncology clinic, the patient complained of further increase in the size of the mass as well as growing discomfort in the area. Physical exam revealed a large, firm, discrete but nontender left buttock mass, measuring approximately 14 × 10 cm (Figure 1). There was no other palpable lymphadenopathy or hepatosplenomegaly, and the rest of his physical and neurologic exam was normal. A CT scan of the chest, abdomen, and pelvis was performed revealing a massively enlarged left gluteus maximus muscle measuring 14.4 × 9.7 cm with homogeneous attenuation and no drainable fluid collection that was extending into the sacrosciatic notch, sacroiliac joint, and with epidural extension into the sacral foramen (Figure 2). There were no other abnormal findings. A core needle biopsy was performed, and pathology revealed a diffuse infiltrate of small lymphocytes that was negative for CD5, CD10, CD23, bcl-6, cyclin D1, and positive for CD20 and CD43, consistent with marginal zone lymphoma (Figure 3). The patient denied weight loss, fevers, or night sweats. A bone marrow biopsy was performed and showed no evidence of lymphoma. Laboratory evaluation including a CBC, comprehensive metabolic panel, LDH, and hepatitis serologies were negative.
Due to increasing discomfort and moderate difficulty in ambulation attributable to the mass, treatment comprising four cycles intravenous rituximab 375 mg/m2, cyclophosphamide 750 mg/m2, vincristine 1.4 mg/m2 given on Day 1 and oral prednisone 40 mg/m2 daily from Days 1 to 5 (R-CVP), was begun. The patient tolerated treatment well with no adverse effects. There was complete resolution of the mass after two 21-day cycles of R-CVP.
Marginal zone lymphomas (MZL) are a group of distinct entities including nodal MZL, extranodal MZL, and splenic MZL. They all share a similar immunophenotype, being positive for B cell markers CD19, CD20, and CD22, and negative for CD5, CD10, and usually CD23. MZLs are often indolent malignancies and present with localized disease. Risk factors associated with the development of these malignancies include autoimmune diseases such as Sjogren's syndrome and Hashimoto's thyroiditis, and various infectious agents including Helicobacter pylori, Chlamydia psittaci, Borrelia burgdorferi, Campylobacter jejuni, and even the human immunodeficiency and hepatitis C viruses. Extranodal MZLs constitute about 5% of all Non-Hodgkin's lymphomas. Most extranodal MZL patients present with stage I or II disease and B-symptoms are uncommon. Extranodal MZLs most commonly involve the gastrointestinal tract (stomach most commonly), lung, lacrimal and salivary glands, skin, thyroid, dura, and breast where mucosa-associated lymphoid tissue is abundant. Standard treatment for extranodal MZLs has not yet been established due to the small number of studies in the literature, and thus is highly individualized. For patients with localized disease, locoregional radiation therapy is appropriate. Patients with advanced disease are managed similarly as patients with follicular lymphoma with conventional chemoimmunotherapy.
Primary skeletal muscle involvement with lymphoma is exceedingly rare; most of the cases described in the literature are of the diffuse large B-cell type and is thought to carry a poor prognosis. The patient described in the case had a complete response after treatment and experienced no adverse events. Although MZL of the extra-ocular muscles have been described in the literature, to the authors' knowledge, this is the first report of marginal zone lymphoma of the gluteal muscle.Photograph of left gluteal muscle prior to initiating chemotherapy.Photograph of left gluteal muscle prior to initiating chemotherapy.CT scan image of left gluteal mass.CT scan image of left gluteal mass.Core biopsy. H&E, 20X.Core biopsy. H&E, 20X.

Disclosures:
No relevant conflicts of interest to declare.