Oxford Case Histories in Oncology

Case 27

Solitary plasmacytoma

Isabella Maund and Michael Williams

Case history

A 50-year-old firefighter presented with a 2-month history of progressive lower back pain. Examination revealed no focal weakness of his legs but limited mobility secondary to pain. Sensation was normal and no bladder or bowel disturbance was noted. An MRI scan was performed (Fig. 27.1).

Fig. 27.1

Question

1. Describe the imaging findings in Figure 27.1 and your differential diagnosis.

Answer

1. Describe the imaging findings in Fig. 27.1 and your differential diagnosis.

There is an extensive destructive mass involving the L4 vertebral body, which is fractured and reduced in height. There is a large soft tissue component compressing the theca. No other lesions are obvious within the included images.

The differential diagnosis of a solitary tumour of the spine includes metastatic carcinoma, lymphoma, plasma cell neoplasia, primary malignant spinal tumours such as chondrosarcoma, and benign tumours such as a haemangioma.

Percutaneous biopsy of the spinal lesion performed under CT guidance revealed a neoplasm of dyscohesive cells with eccentric round nuclei. Immunohistochemical staining was positive for CD138 and kappa light chain, suggestive of a plasma cell neoplasm.

Questions

2. What staging investigations would you perform?

3. What are the criteria for diagnosing solitary plasmacytoma of bone?

4. What treatment do you suggest if solitary plasmacytoma of bone is diagnosed?

Answers

2. What staging investigations would you perform?

The majority of patients with plasma cell neoplasia will have generalized disease, i.e. multiple myeloma, at the time of diagnosis. A few patients (<5%) will, however, present with truly isolated disease in the form of a solitary bone lesion or rarely a soft tissue mass of monoclonal plasma cells. Staging is required to establish whether apparently isolated lesions are truly solitary and to determine whether there is evidence of bone marrow involvement or end-organ damage, thus essential investigations include:

♦ FBC

♦ biochemical screen including renal function and corrected calcium

♦ serum immunoglobulin levels

♦ serum and urine protein electrophoresis and immunofixation

♦ serum free light chain analysis

♦ bone marrow aspirate and trephine

♦ full skeletal survey

♦ MRI of the spine and pelvis.

Standard X-rays have conventionally been used for the skeletal survey and are still employed in current trials. Other imaging modalities, such as whole-body low-dose CT and whole-body MRI, have the advantage of greater sensitivity and have been adopted in many centres. FDG-PET may have a role in selected patients and is useful in the assessment of response following treatment; however, at present PET is not considered a routine investigation.

3. What are the criteria for diagnosing solitary plasmacytoma of bone?

Solitary plasmacytoma of bone is rare, with an incidence rate of 0.34/100,000 person-years. There is a preponderance in men (M:F 2:1), and a median age of presentation of 55 years. It most commonly affects the axial skeleton, especially the vertebrae. Diagnosis requires evidence of a solitary bone lesion which on biopsy shows infiltration by plasma cells, without evidence of systemic disease (Table 27.1).

4. What treatment do you suggest if solitary plasmacytoma of bone is diagnosed?

Radical radiotherapy remains the cornerstone of management of solitary plasmacytoma of bone. In cases of spinal involvement, neurosurgical/orthopaedic opinion should be sought, as there may be a role for surgical intervention in the form of stabilization procedures for loss of structural integrity or neurological compromise. Outside of these indications, surgical intervention is not recommended. Where surgery is required, it should be used in conjunction with radiotherapy; the relative timings of treatments must be decided individually for each patient.

Table 27.1 Diagnostic criteria for solitary plasmacytoma of bone, extramedullary plasmacytoma, and multiple solitary plasmacytomas

*A small M-component may sometimes be present in blood or urine.

Adapted with permission from The International Myeloma Working Group. Criteria for the classification of monoclonal gammopathies, multiple myeloma and related disorders: a report of the International Myeloma Working Group, British Journal of Haematology, Volume 121, pp. 749–757, Copyright © 2003, John Wiley and Sons.

There is limited evidence from small studies that the use of adjuvant chemotherapy may improve the duration of remission and survival. However, at present, there is insufficient evidence to recommend the routine use of adjuvant or maintenance chemotherapy following radiotherapy for solitary plasmacytoma of bone.

The patient was referred to spinal surgeons who recommended L4 laminectomy and stabilization. This resulted in immediate, dramatic benefit in terms of pain control and mobility.

Routine blood tests including FBC, renal function, and calcium levels were unremarkable. Both skeletal survey and bone marrow trephine were negative. Bence-Jones proteinuria was negative with a pre-operative serum M band of 7g/L. A diagnosis of solitary plasmacytoma of bone was therefore confirmed and the patient was consented to undergo radical radiotherapy.

Questions

5. Describe the radiotherapy technique and dose that you would recommend for this patient.

6. What difficulties do you anticipate with delivery of the radiotherapy plan and what late complications should the patient be consented for?

7. What is the prognosis of this patient?

Answers

5. Describe the radiotherapy technique and dose that you would recommend for this patient.

Patients were conventionally planned and treated prone; however, a supine position is acceptable and may be more comfortable for the patient. Appropriate immobilization, including hip fixation and indexed knee rests, is required. Treatments should be planned using three-dimensional CT planning with access to pre-operative MRI images.

An example plan demonstrating the principle of plasmacytoma radiotherapy is shown in Fig. 27.2. The GTV includes the mass and all of the involved bone. This has been grown by 10mm to form a CTV. A 5mm PTV margin has been used as the patient was treated using daily image guidance. The kidney can be seen closely adjacent to the CTV.

Fig. 27.2 (See also colour plate section)

Tumour bulk has been established as the most important factor influencing local control. Current guidelines recommended a dose of 40Gy in 20 fractions for treatment of solitary plasmacytoma of bone of 5cm or less and that higher doses of up to 50Gy in 25 fractions are considered for tumours of over 5cm.

6. What difficulties do you anticipate with delivery of the radiotherapy plan and what late complications should the patient be consented for?

The OAR most likely to influence radiotherapy delivery in this case is the kidney, and patients should be consented for late effects of renal damage including malignant hypertension, anaemia, and renal dysfunction. According to current recommendations, for partial bilateral kidney irradiation the mean dose should be kept below 15–18Gy and the V20 (the volume of kidney receiving 20Gy) below 32%. Dimercaptosuccinic acid scanning to determine differential renal function may be useful for treatment planning, allowing relative sparing of a dominant kidney if present.

It is estimated that a dose of 50Gy to the spinal cord is associated with a 0.2% risk of myelopathy. Patients should be consented for the potentially severe effects of radiation-induced spinal cord injury including pain, paraesthesia, and paralysis. Other important late effects include vascular complications, including spinal cord haemorrhage, and the risk of radiation-induced secondary malignancy.

7. What is the prognosis of this patient?

Excellent rates of local control in excess of 80% can be achieved with radiotherapy alone. Unfortunately, however, >75% of patients with apparent solitary plasmacytoma of bone will ultimately progress to multiple myeloma after a median duration of 21 months (range 2–135 months). The median OS is 7.5–12 years.

Further reading

Dimopoulos MA, Moulopulos LA, Maniatis A, et al. Solitary plasmacytoma of bone and asymptomatic multiple myeloma. Blood 2000; 96: 2037–2044.

Hughes M, Soutar R, Lucraft H, et al. Guidelines on the diagnosis and management of solitary plasmacytoma of bone, extramedullary plasmacytoma and multiple solitary plasmacytomas: 2009 update. London: British Committee for Standards in Haematology; 2009.

Knobel D, Zouhair A, Tsang RW, et al. for the Rare Cancer Network. Prognostic factors in solitary plasmacytoma of the bone: a multicenter Rare Cancer Network study. BMC Cancer 2006; 6: 118–127.

Lütje S, de Rooy JWJ, Croockewit S, et al. Role of radiography, MRI and FDG-PET/CT in diagnosing, staging and therapeutical evaluation of patients with multiple myeloma. Annals of Hematology 2009; 88: 1161–1168.

Soutar R, Lucraft H, Jackson G, et al. Guidelines Working Group of the UK Myeloma Forum, British Committee for Standards in Haematology, British Society for Haematology. Guidelines on the diagnosis and management of solitary plasmacytoma of bone and solitary extramedullary plasmacytoma. British Journal of Haematology 2004; 124: 717–726.

The International Myeloma Working Group. Criteria for the classification of monoclonal gammopathies, multiple myeloma and related disorders: a report of the International Myeloma Working Group. British Journal of Haematology 2003; 121: 749–757.