Acute lymphocytic leukemia (ALL) is one of the four main types of leukemia.

“Acute” means progressing quickly without treatment. “Lymphocytic” refers to lymphocytes, immature white blood cells. About 4,000 people in the United States are diagnosed with ALL each year — most of them are younger than 18 years old.

Philadelphia chromosome (Ph+) ALL is a specific type of ALL characterized by a genetic mutation called the Philadelphia chromosome.

Despite ALL being the most common childhood cancer, Ph+ makes up a small percentage of childhood ALL cases. Only about 1 to 5 percent of children with ALL have Ph+ compared to 11 to 30 percent of adults with ALL.

This rare condition goes by several other names, including Ph+ or PH+ acute lymphoblastic leukemia.

Keep reading to learn more about Ph+, including how it differs from other ALL types, risk factors, and treatment options.

Ph+ is a subtype of ALL where leukemia cells contain a genetic mutation called the Philadelphia chromosome, named after its place of discovery. People with other types of ALL don’t have this chromosome.

Human cells usually have 23 pairs of chromosomes that contain genetic information. The Philadelphia chromosome is a shortened version of chromosome 22. It forms when a gene generally found on chromosome 9 called ABL attaches to the BCR gene on chromosome 22. This fusion causes the formation of a new gene called BCR-ABL.

BCR-ABL makes a protein called tyrosine kinase. This protein causes leukemia cells to grow uncontrollably and crowd out healthy white blood cells.

Along with people with Ph+, almost all people with chronic myeloid leukemia have the Philadelphia chromosome.

Several genetic mutations have been identified in people with either type of ALL, such as:

  • a missing chromosome 7
  • an extra chromosome 8
  • abnormal changes in genes on chromosomes 4 and 11
  • a less than usual number of chromosomes
  • a more than usual number of chromosomes
  • abnormal changes in genes on chromosomes 10 and 14

If Philadelphia chromosomes aren’t present, the disease is known as Ph-negative (Ph-) ALL. Determining which type of ALL you have can help a doctor determine your prognosis and the best treatment options.

Having Ph+ was traditionally associated with a less positive outlook. But the recent development of a targeted therapy called tyrosine kinase inhibitors (TKIs) has improved the outlook. Treatment is typically less effective in adults over 60 years old.

Once you’re diagnosed with ALL, a healthcare professional can perform specialized tests to see which subtype you have.

A small blood sample is analyzed in a lab. A bone marrow aspiration and a biopsy will likely be performed. This is done by extracting a small sample of bone marrow, usually from your hip.

One of several types of laboratory tests may then be used to analyze your samples:

  • Cytogenetics. In conventional cytogenetics, DNA is analyzed under a microscope to examine cells as they’re dividing.
  • Fluorescent in situ hybridization (FISH) test. This test uses special fluorescent dyes to identify the BCR-ABL gene. These dyes attach to certain genes but not others.
  • Polymerase chain reaction (PCR) test. A PCR test can detect even small amounts of Philadelphia chromosomes not identifiable with other tests.

Children are more likely to be diagnosed with ALL — and only 25% of ALL cases in adults are diagnosed as Ph+.

ALL is slightly more common in:

  • males than females
  • whites than African Americans

Some environmental factors that can increase your risk for ALL include:

  • exposure to benzene in substances like sunscreen
  • ionizing radiation
  • previous chemotherapy and radiotherapy

ALL is more common among children with conditions such as:

  • Down syndrome
  • neurofibromatosis
  • Bloom syndrome
  • ataxia-telangiectasia

Treatment for Ph+ generally consists of a targeted therapy called TKI combined with a mixed chemotherapy regime. Then it’s followed by an allogeneic bone marrow transplant.

This type of transplant is done by taking bone marrow cells from a donor who’s a close genetic match to you and transplanting the cells into your bone marrow to replace your damaged cells. The National Comprehensive Cancer Network recommends these transplants for children and adults after successful treatment.

TKIs block the ability of the protein BCR-ABL to send signals that lead to the formation of leukemia cells. Imatinib is the most commonly used TKI. Dasatinib and ponatinib are also used. One clinical trial is looking at the effectiveness of ponatinib alongside imatinib.

The outlook of Ph+ has improved since TKIs have been used. Before TKIs were available, the 3-year overall survival rate in adults with Ph+ who received chemotherapy was less than 20 percent.

A 2015 study in the American Journal of Cancer Research found that chemotherapy combined with the TKI imatinib raised the remission rate — meaning that the cancer was gone completely — in adults to more than 90 percent and the 5-year overall survival rate to 43 percent.

Chemotherapy for ALL usually lasts about 2 to 3 years. The most intense treatments happen in the first few months.

Dealing with a Ph+ diagnosis can be difficult, but the use of TKIs has significantly improved its outlook.

Children usually have a higher chance of survival, but survival rates for everyone are rising. Being younger than 30 and having a white blood cell count of less than 30,000 can improve your outlook.

Ask a healthcare professional about clinical trials that you may qualify for. Some clinical trials give you access to state-of-the-art treatments that otherwise wouldn’t be available.