This observational study aims to evaluate the feasibility of assembling a retrospective cohort of formalin-fixed paraffin-embedded (FFPE) tissue samples from patients with extramedullary multiple myeloma, together with their associated clinical and pathological data. The study will determine whether these archived samples are suitable for exploratory biomarker assessment.

No intervention is performed. All FFPE samples and clinical data originate exclusively from routine diagnostic procedures and will be analyzed retrospectively for research purposes.

This retrospective observational study aims to determine the feasibility of assembling a cohort of formalin-fixed paraffin-embedded (FFPE) tissue samples from patients with extramedullary multiple myeloma and linking these materials with associated clinical and pathological data. All samples originate from routine diagnostic procedures performed as part of standard clinical care; no prospective interventions or additional tissue collection are involved.

The study evaluates whether archived FFPE specimens and corresponding clinical information can be systematically identified, retrieved, and abstracted using a predefined standardized workflow. Histopathological review and immunohistochemical markers routinely assessed during diagnostic work-up (CD138, CD56, MUM1, light chains) will be used to confirm the diagnosis and describe tumor features. Feasibility will be defined by the proportion of screened cases for which both adequate FFPE material and sufficient clinical data are available to allow inclusion.

The purpose of the study is to generate a structured dataset enabling future biomarker research and to assess whether the operational workflow used for case identification, data abstraction, and sample processing can be reliably scaled for larger retrospective cohorts.

Inclusion Criteria:

• Adult patients with histologically confirmed extramedullary myeloma (excluding plasmacytoma).
• Availability of a representative FFPE block from a surgical specimen.
• Diagnosis established within the past 10 years.
• Availability of associated clinical and follow-up data.

Exclusion Criteria:

• Patients with plasmacytoma only.
• Insufficient or non-representative FFPE material.
• Missing key diagnostic or clinical data.

The study population consists of adult patients diagnosed with extramedullary myeloma (excluding plasmacytoma) for whom a representative FFPE block from a surgical specimen was obtained as part of routine clinical care within the past 10 years. Only cases with sufficient clinical, pathological, and follow-up data are included. All samples were collected outside the context of research activities.