Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults, affecting B lymphocytes, a type of white blood cell. This slow-growing cancer involves an uncontrolled accumulation of these cells. Like many cancers, CLL often involves genetic changes. Among these, a specific alteration known as 13q deletion is frequently observed and holds significance in CLL.
Understanding 13q Deletion
A “deletion” refers to the loss of genetic material from a chromosome. In CLL, “13q” denotes the long arm (q arm) of chromosome 13, with the deletion typically occurring at band 14 (13q14). This is the most common chromosomal abnormality in CLL patients, found in over 50% of cases.
The loss of this region is significant because it contains tumor suppressor genes, notably miR-15a and miR-16-1. These microRNAs regulate cell death in B lymphocytes. Their absence, due to the deletion, contributes to the uncontrolled proliferation and extended survival of B cells, a hallmark of CLL. The size of the deleted region on 13q can vary. Smaller deletions often encompass only the MIR15A/MIR16-1 locus, while larger deletions might involve additional genes, including RB1.
Impact on Disease Progression and Outlook
The presence of an isolated 13q deletion (the sole genetic abnormality detected) is considered a favorable prognostic marker in CLL. Patients with this deletion often experience a more indolent disease, characterized by slower progression, leading to a longer time before treatment is necessary.
A favorable prognosis means the disease behaves less aggressively compared to CLL cases with other genetic abnormalities, such as deletions on chromosome 17p or 11q, or trisomy 12. For instance, median survival in CLL patients with 13q deletions has been reported around 133 months. However, the clinical course can still vary, even with 13q deletion, influenced by factors like deletion size or percentage of affected cells. Large 13q losses involving the RB1 gene are associated with a shorter time to first treatment and overall survival compared to smaller deletions.
Detection and Treatment Approaches
The primary method used to detect the 13q deletion in CLL is Fluorescence In Situ Hybridization (FISH) testing. This test targets specific genes or regions frequently affected in CLL, allowing for the identification of chromosomal alterations. FISH testing is typically performed at diagnosis or when treatment is considered, as it helps classify CLL patients into different prognostic groups.
While an isolated 13q deletion is a favorable indicator, treatment decisions for CLL are complex and depend on several factors. These include the patient’s symptoms, the rate of disease progression, and the presence of other genetic markers. The 13q deletion might influence the choice of specific therapies, as research into this deletion has provided insights into molecular pathways relevant to CLL treatment. However, it does not mean that treatment will never be needed, but rather that the disease may be monitored for a longer period before intervention is required.