Plasma cell neoplasms are divided into two different categories: multiple myeloma and solitary plasmacytoma. Solitary plasmacytomas are most commonly found in the bone, however they can also be extramedullar. 90% of all EMPs are found in the head and neck region, particularly the upper respiratory and digestive tracts. Other locations include the gastrointestinal tract, central nervous system, skin and, rarely, the testis. EMPs account for only 3% of plasma cell malignancies. The mean age of diagnosis is 55 to 60 years, with a male to female ratio of two to one [
1‐
3]. The diagnosis of EP requires many diagnostic studies including CBC with differential and smear, complete metabolic panel, SPEP with immunofixation of immunoglobulins, biopsy of the lesion, bone aspiration and biopsy, and metastatic bone survey by positron emission tomography (PET) with computed tomography (CT) or magnetic resonance imaging (MRI). By definition, patients with EMP cannot have symptoms of multiple myeloma including anemia, hypercalcemia, or renal insufficiency. The lesion should have evidence of clonal plasma cells, and the bone marrow biopsy must contain no clonal plasma cells. Some patients may have small amounts of monoclonal protein, usually IgA, in the serum or urine. The marrow of some patients may have up to 10% clonal plasma cells. These patients are considered to have both EMP and MGUS. These patients have higher risk of progressing to multiple myeloma [
3,
6]. The treatment of these tumors is either radiation therapy or surgical resection. Adjuvant radiation or chemotherapy does not improve the outcome. In patients with incomplete resection, local radiation is the best treatment. Less than 10% of patients develop local recurrence. These patients have high rates of progression to multiple myeloma, up to 15% [
7]. The overall 10-year survival for patients with EMP is 70% [
3].
Isolated testicular plasmacytoma accounts for only 0.03-0.1% of all testicular tumors [
1,
7]. The vast majority of patients with testicular plasmacytoma either have disseminated disease at the time of diagnosis, or develop disseminated disease later in life [
1,
2,
5]. This case is therefore unusual due to the primary nature of the plasmacytoma within the testis. The age of diagnosis ranges from 26 to 83 years of age, although the mean age of diagnosis in 55 to 60 years old [
4]. The incidence of plasmacytoma also increases with age [
8]. Patients commonly present with a firm testicular mass, which may or may not be tender. Patients with disseminated disease may also present with symptoms of multiple myeloma such as back pain. On gross examination, the tumors are soft, fleshy, and white or grey in color [
4]. On ultrasound, plasmacytoma of the testicle can be either homogeneous or heterogeneous, and typically hypoechoic. Hyperemia on Doppler imaging has also been observed in these tumors, although hyperemia is also characteristic of many types of testicular tumors [
5,
9]. On microscopic examination, the tumor appears as sheets of atypical plasma cells with varying degrees of differentiation [
5]. Plasmacytomas can be mistaken for other types of tumors, including seminoma, lymphoma and metastatic melanoma [
2,
4]. In order to make accurate diagnosis, immunologic staining for CD 138, CD 79a and monoclonal antibody VS 38 can be used [
4]. Additionally, immunostaining will reveal IgG, IgD or IgA light chains; IgA being the most common [
7]. The treatment of choice for testicular plasmacytoma is radical orchiectomy. In addition, these tumors are highly radiosensitive so a combination of surgery and radiation can be implemented. For patients with residual disease after surgery, or recurrent or refractory disease, radiation can be used as well [
4]. The overall prognosis for patients with testicular plasmacytoma is poor, with high rates of progression to multiple myeloma. Because of the high rates of progression, these patients require close monitoring and long-term surveillance. There are no established guidelines as to which tests are appropriate for surveying for metastatic disease, or for the frequency or duration of surveillance. A common approach includes a combination of periodic history and physical exam, laboratory tests (urine and serum protein electrophoresis with immunofixation, CBC, serum creatinine, serum calcium) and imaging such as PET with or without CT or MRI at lengthening intervals.