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paraprotein concentration was 73 g/L, the free lambda light chain value was 2190 mg/L, and the
uninvolved/involved light chain ratio was 0. The bone marrow biopsy demonstrated infiltration with 90% of
CD138+, lambda +, kappa- plasma cells. Unfortunately, cytogenetic analysis was not performed for
technical reasons at the time of diagnosis. Initially, two cycles of the VCD (bortezomib, cyclophosphamide,
and dexamethasone) regimen with bisphosphonates were administered. Due to symptoms and signs of
pneumonia, a computed tomography (CT) of the thorax was performed, determining a large tumor of the
posterior mediastinum infiltrating Th6-Th12 vertebrae and prolapsing into the spinal canal [Figure 1].
Surgical treatment and biopsy confirmed a plasmacytoma consisting of lambda-positive plasma cells
[Figure 2A]. Radiotherapy of the mediastinal plasmacytoma and infiltrated vertebrae Th7-Th9 was
performed and a second line of treatment with the DVd (daratumumab, bortezomib, and dexamethasone)
regimen was administered. After only four cycles, further progression was observed (increase in serum
paraprotein). Thus, a third line of treatment started with the KRd (carfilzomib, lenalidomide, and
dexamethasone) regimen. After four cycles of therapy, radiological imaging showed significant regression of
the residual thoracic extramedullary tumor mass without protrusion into the spinal canal. A humoral
reevaluation of the disease showed a very good partial remission. Since the general condition of the patient
was not good enough to perform an autologous hematopoietic stem cell transplantation, the KRd regimen
was continued until the ninth cycle, when a new progression of disease occurred (pathological bone
fractures of the ribs and progression of the mediastinal plasmacytoma with large pleural effusions, but
without an increase of paraprotein concentration or involved free light chain in serum or urine). Further
palliative radiotherapy was done, and chemotherapy with the VAD (vincristine, adriamycin, and
dexamethasone) regimen in combination with pomalidomide was started. After five cycles of this therapy,
severe infectious complications and sepsis occurred without significant tumor regression. The patient was
discharged from the hospital with the best supportive care recommendations after approximately two years
from diagnosis. Interestingly, while extramedullary tumor has progressed, bone marrow biopsy showed no
plasma cell infiltration.

MVD in mediastinal paraosseous plasmacytoma was 32, while the percentage of OPN-positive cells was
around 70% [Figures 2B and C].

Case 2
Our second patient, a 72-year-old female with a previous history of arterial hypertension, ischemic heart
disease, and percutaneous coronary intervention, has been diagnosed as MM, light chain disease, lambda,
ISS III, with symptomatic anemia and extensive bone marrow infiltration with 80% of CD138+, lambda+,
kappa- plasma cells. The serum free lambda light chain value was 38 mg/L and the uninvolved/involved
light chain ratio was 0.085. Unfortunately, cytogenetic analysis was not performed for technical reasons at
that time. Initially, the patient refused the proposed treatment. A year after the diagnosis was made, the
patient developed intermittent headaches and vision impairment in the right eye. Brain magnetic resonance
imaging showed a 62 mm × 37 mm large tumor that infiltrated the right orbit, eroded the skull base,
protruded into the middle cranial fossa suppressing the brain, and infiltrating the sphenoid and maxillary
sinus [Figure 3]. PET-CT confirmed a high metabolic activity of the malignant process infiltrating the
viscerocranium, as well as osteolytic lesions in the right iliac bone.

Pathohistological diagnosis established by endoscopic biopsy of the right maxillary sinus showed infiltration
of MM [Figure 2D]. There were no malignant cells found in the cerebrospinal fluid. Considering possible
side effects of radiotherapy (loss of vision on the right eye), the patient was not inclined to it. She was
initially treated with eight cycles of the VCD protocol with bisphosphonates and showed partial remission.
Brain CT also showed a significant reduction of the tumor. Maintenance therapy with bortezomib and
dexamethasone was continued. Unfortunately, four months after maintenance therapy was started, the