Objective 1: To test whether treatment with plasma exchange improves renal recovery in patients with light chain cast nephropathy Objective 2: To compare renal outcomes among patients treated with plasma exchange versus daratumumab-based regimens versus non-daratumumab based-regimens.

Objective 1:

We will collect data from patients treated with plasma exchange from major centers across the United States to investigate whether plasma exchange improves renal outcomes.

Specifically, we will collect data on at least 150 patients treated with plasma exchange along with 300 control patients not treated with plasma exchange.

Objective 2:

We will compare renal outcomes among patients with light chain cast nephropathy and AKI treated with plasma exchange (n=150) versus daratumumab based regimen (eg Dara-CyborD) (n=150) versus other novel regimens (e.g., CyborD or another non-daratumumab-based regimen) (n=150). We will examine whether patients who receive dara-based regimens are more likely to have renal recovery compared to patients who do not receive dara-based regimens and to patients who receive plasma exchange. Given the infrequency with which plasma exchange is performed on a single-center level, we will compare outcomes among patients treated with plasma exchange, utilizing data from the multicenter study to those patients who were treated with daratumumab-based regimens without plasma exchange versus non- daratumumab-based regimen.

Inclusion Criteria for Plasma Exchange-Treated Patients:

1. Adult (≥18 years old)
2. Either a new diagnosis of multiple myeloma confirmed by bone marrow plasmayctosis >10% or acute relapse of multiple myeloma
3. Light chain cast nephropathy, with involved light chain >500 mg/L
4. Acute kidney injury, defined as ≥1.5-fold rise in SCr from baseline (as defined in study outcomes) or the need for renal replacement therapy (RRT).
5. Treated with at least 1 round of plasma exchange within 30 days of diagnosis of cast nephropathy
6. Treated with plasma exchange in 2010 or later

Inclusion Criteria for Control Patients:

1. Adult (≥18 years old)
2. Either a new diagnosis of multiple myeloma confirmed by bone marrow plasmayctosis >10% or acute relapse of multiple myeloma
3. Light chain cast nephropathy, with involved light chain >500 mg/L
4. Acute kidney injury, defined as ≥1.5-fold rise in SCr from baseline or the need for renal replacement therapy (RRT)

Exclusion Criteria for Both Plasma Exchange-Treated Patients and Control Patients:

1. Patients with end stage kidney disease
2. Patients with amyloidosis or monoclonal immunoglobulin deposition disease
3. Patients with chronic lymphocytic leukemia, plasma cell leukemia, or Waldenstrom's
4. Moribund condition (e.g., patients who died within 48 hours of initiation of plasma exchange)
5. Active urinary tract obstruction on renal imaging
6. Patients with significant albuminuria (≥2+ on urinary dipstick or >10% fraction on UPEP)
7. Patients with other biopsy-proven causes of AKI (non-cast nephropathy lesions)
8. Patients who did not receive clone-directed therapy for myeloma
9. Patients who received plasma exchange >30 days from the time of diagnosis of cast nephropathy

Patients with multiple myeloma and clinically-suspected or biopsy-proven light chain cast nephropathy