Chronic Disease Surveillance and Research Branch

Ladera Ranch Cancer Concern

FAQ: Cancer Concerns in the Ladera Ranch Community

The health and well-being of California's children is the California Department of Public Health's (CDPH) highest priority. CDPH takes the concerns raised by Ladera Ranch families and community members seriously, and we are committed to a thorough, transparent assessment of cancer incidence in the area.

CDPH's California Cancer Registry (CCR) is known as one of the top cancer registries in the world. CCR, in coordination with our regional partner, the Cancer Registry of Greater California, is reviewing cancer incidence data for the Ladera Ranch area in Orange County in response to community concerns regarding several cancer types, including a rare childhood cancer, Ewing sarcoma. CDPH currently estimates the assessment will be completed in fall 2026, although the timeline may change based on the scope and complexity of the review and any additional information that may need to be evaluated.
CDPH will share findings as soon as they're available, and continue coordinating with local, state, and federal partners throughout this process.

What we know

Community concerns prompted this assessment. Ladera Ranch residents raised concerns about the incidence of childhood cancers in their community and asked for more information and answers. This assessment is a direct response to that.
Pesticide use is a specific concern raised by residents. We are aware that pesticide use in the community is a central question. Because of this concern, the assessment looks specifically at cancer types that research has linked to pesticide exposure, and asks whether those cancers occur more often in Ladera Ranch than expected. The assessment measures how often these cancers occur.
A 2024 county-level review was inconclusive. That analysis did not find an unusual pattern at the county level, but the data available at the time was limited, which is why a more focused assessment of Ladera Ranch specifically is now underway.
Assessments of unusual cancer patterns rarely identify a cause. National data show that confirming an increase in cancer and identifying its cause is rare. A 2012 review of U.S. cancer cluster investigations during a 20-year period found that an increase in cancer was confirmed for only about 13% of the cancer types studied. Only 1 of the 428 investigations identified a clear cause.
At this time, our colleagues at CalEPA (California Environmental Protection Agency) and its Boards, Departments, and Offices have not identified any immediate environmental hazards. CalEPA and CDPH will continue to coordinate closely with CalEPA’s Department of Pesticide Regulation, the Orange County Agricultural Commissioner, U.S. EPA, and local health officials.

What we don't know

We don't yet know whether the incidence of Ewing sarcoma and other cancer types is higher than expected in the Ladera Ranch community. CDPH now has case data through 2023 and census-tract-level data, allowing for a more focused assessment of Ladera Ranch that was not previously possible in 2024.
We don't know whether environmental factors can cause Ewing sarcoma or related types of cancer. According to the American Cancer Society, no known lifestyle or environmental cause of Ewing sarcoma has been identified. This is a gap in the broader scientific understanding of the disease, and closing it will require sustained research by scientists, public health agencies, and the federal government over the years to come.
We don't yet know whether pesticides or other chemicals created an exposure risk in Ladera Ranch. CalEPA and the Orange County Agricultural Commissioner are gathering additional information on this question.

How are we finding answers?

CDPH is conducting a cancer concern assessment as quickly as possible. The assessment will evaluate whether the number of cancers diagnosed in the Ladera Ranch area is higher than what would be expected based on population-based cancer registry data. This work is underway now and expected to be complete in fall 2026, although the timeline may change based on the scope and complexity of the assessment and any additional information that may need to be evaluated. If that timeline changes, we will tell the community why.
CDPH is following established national guidelines. CDPH is using the Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry (CDC/ATSDR) Guidelines for Examining Unusual Patterns of Cancer and Environmental Concerns, the same framework public health agencies nationwide used to evaluate cancer concerns.
CDPH is coordinating directly with state and local partners, including CalEPA. A cancer concern assessment can determine whether cancer incidence appears higher than expected but cannot by itself determine whether an environmental exposure caused that increase. CDPH is consulting and sharing information with local and state partners in parallel, including the CalEPA.

What is CalEPA doing?

While federal (CDC/ATSDR) guidance does not recommend launching an environmental assessment until evidence shows an increase in cases, CalEPA recognizes the community's concerns about exposure to environmental harms. In response to concerns about pesticide use in the Ladera Ranch region, the Department of Pesticide Regulation (DPR) and the Orange County Agricultural Commissioner (CAC) are reviewing local pesticide use to determine if there are any possible violations of state or federal law. This includes interviewing pesticide companies, reviewing pesticide use and training records, and observing local pesticide applications.

Additional Q&A

Whom should I contact if I am a researcher interested in using CCR data?

Researchers interested in using CCR data for a scientific health study should first review the CCR's How to Request CCR Data webpage. Under California law, access to confidential CCR data is limited to people with a valid scientific interest who are conducting demographic, epidemiologic, or similar health studies, meet CDPH's qualifications, and agree in writing to protect confidentiality.

The Committee for the Protection of Human Subjects (CPHS), CCR's institutional review board, requires a letter of support from CCR. To request the letter, researchers must provide CCR with a draft CPHS application and a list of the CCR variables they plan to request at least one month before the CPHS application deadline. CCR and CPHS are separate entities. Questions about CCR data requests may be sent to ccrresearch@health.ucdavis.edu. Questions about IRB Manager or the CPHS process may be sent to cphs@chhs.ca.gov.

How can I contact CDPH with questions about the assessment?

For questions about the Ladera Ranch community cancer concern assessment, contact the California Cancer Registry at cdsrbhelp@cdph.ca.gov. Please allow 7 to 10 business days for a response. Do not send medical records or other private health information by regular email. Reporters and other members of the media should contact media@cdph.ca.gov.

What is the smallest geographic area CCR can use to analyze cancer incidence?

The census tract is generally the smallest standard geographic unit the California Cancer Registry uses for population-based cancer-incidence analyses. Like other population-based cancer registries, CCR records a person's residential address at the time of diagnosis and uses that address to assign the case to a standardized census geography.

Cancer rates require both the number of diagnosed cases and a corresponding population estimate. The National Cancer Institute provides population estimates at the county and census-tract levels, allowing registries to calculate incidence rates and expected numbers of cases for those geographic areas. Census tracts are also used nationally for small-area cancer surveillance under the North American Association of Central Cancer Registries standards.

CCR generally cannot reliably calculate cancer incidence rates for individual streets, schools, homeowners' association boundaries, or other very small or informally defined areas because compatible population estimates may not be available. Very small areas can also produce statistically unstable estimates and increase the risk of identifying individuals. For those reasons, census tracts may need to be combined, and some results may need to be suppressed to protect patient confidentiality.

Could a formal epidemiologic study examine possible environmental causes?

Yes, but it is critical to first determine whether the number of cancers diagnosed in the defined area is higher than expected before attempting to identify any shared environmental exposures. This stepwise approach to assessing reported cancer concerns is consistent with the approach described in the Centers for Disease Control and Prevention (CDC) and the Agency for Toxic Substances and Disease Registry (ATSDR) Guidelines for Examining Unusual Patterns of Cancer and Environmental Concerns.

How are environmental concerns addressed in cancer concern assessments in California?

The cancer concern assessment and the evaluation of environmental concerns are related but separate activities. A registry-based assessment can determine whether cancer incidence is higher than expected, but it cannot determine whether pesticides or another environmental exposure caused the cancers.
The Centers for Disease Control and Prevention (CDC) and the Agency for Toxic Substances and Disease Registry (ATSDR) guidelines do not recommend launching an environmental assessment until there is evidence that an increase in cancer cases is present. However, the California Environmental Protection Agency (CalEPA) recognizes that the community has raised environmental concerns. At this time, CalEPA and its Boards, Departments, and Offices have not identified any immediate environmental hazards.

In response to concerns about pesticides in the Ladera Ranch area, the California Department of Pesticide Regulation, which is part of CalEPA, is working closely with the Orange County Agricultural Commissioner and the U.S. Environmental Protection Agency to review pest management operations in Ladera Ranch and examine whether they comply with state and federal law.

CalEPA and CDPH will continue to coordinate closely with the Department of Pesticide Regulation, the Orange County Agricultural Commissioner, the U.S. Environmental Protection Agency, and local health officials as the cancer concern assessment and related work proceed.