# Synchronous childhood T-lymphoblastic lymphoma and B-cell precursor acute lymphoblastic leukemia associated with constitutional MMR deficiency syndrome –a case report

## TL;DR

A four-year-old girl developed two rare blood cancers linked to a genetic disorder affecting DNA repair.

## Contribution

This case report highlights the association between CMMRD syndrome and synchronous T-LBL and BCP-ALL in a child.

## Key findings

- Molecular tests confirmed two distinct lymphoid malignancies in a single patient.
- The cancers were linked to constitutional mismatch repair deficiency syndrome (CMMRD).
- The case emphasizes the need for specialized treatment approaches in CMMRD-associated malignancies.

## Abstract

We present a four-year-old girl with synchronous T-cell lymphoblastic lymphoma (T-LBL) and B-cell precursor acute lymphoblastic leukemia (BCP-ALL).Development of two lymphoid malignancies arising from completely different cell lineages was confirmed by molecular tests. The cause of cancerogenesis in this patient was a genetic predisposition resulting from mismatch repair deficiency syndrome (CMMRD). Herein, we present the fatal course of the disorder, challenging treatment decisions and need for special approach to the patients with CMMRD-associated malignant proliferation.