This specialized database includes two additional fields: calculated months from diagnosis to treatment and months since last birthday. Note that the months from diagnosis to treatment field is also now available in the SEER Research Plus databases starting with the November 2021 submission. For date information, such as date of diagnosis, SEER only collects month and year.

Database Details

The database is available in all SEER*Stat sessions for the November 2020 data submission.

  • This database includes all tumor records for 2000-2018.
  • It is identical to the SEER Research Plus database other than two additional calculated months fields: Months From Diagnosis to Treatment and Months Since Last Birthday.

Months From Diagnosis to Treatment

The field is calculated as:

  • Months from diagnosis to treatment = ((Year initial treatment started * 12) + Month initial treatment started) - ((Year of diagnosis * 12) + Month of diagnosis)

Data Limitations and Analytical Considerations

  • Note that days are not available, so this calculation is not exact. If Months > 24 or a component of the date is unknown, a value of blank is assigned. The time is capped at 24 months after diagnosis because after 24 months, this would not typically be the first course of treatment.
  • SEER treatment data is currently limited to the first course treatment modalities, and the time from diagnose to treatment is the time to the first course treatment, which could be chemotherapy, hormonotherapy, radiation therapy or surgery therapy. In some situations, the date represents the time that there was a decision not to treat (for example the time that active follow up was started for prostate cancer).

Certain types of treatment data (i.e., chemotherapy, hormonotherapy, radiation therapy) are incomplete. If the treatment information is missing, the date of treatment is most likely missing as well. Because of the incomplete data, the analysis of the impact of the time from diagnosis to treatment due to a specific type of treatment is possibly biased. For example, if a patient has only surgery collected in SEER with chemotherapy and radiation therapy unknown, it is possible that chemotherapy has been given pre (neoadjuvant) or after surgery (adjuvant), and the time to treatment could be the time to neoadjuvant chemo, not the time to surgery. However, the analysis of overall impact on the first course of treatment is possible. Users are recommended to use cautions in interpreting the results.

Months Since Last Birthday

For date information, such as date of birth or date of diagnosis, SEER only collects month and year. The month of birth is not available for research use because of confidentiality concerns. We calculated a Months Since Last Birthday variable, which can be used in conjunction with the age in years at diagnosis to derive the age in months at diagnosis. This variable is calculated from three intermediate months variables derived using confidential data and these intermediate variables are not available for release but instrumental to the final calculation.

This field and three intermediate variables are calculated as:

  • Intermediate Variables:
    • Birth date in months = (year birth * 12) + month birth, and Diagnosis date in months = (year diagnosis * 12) + month diagnosis.
    • Age in months = diagnosis date in months – birth date in months.
  • Released Variable:
    • Months Since Last Birthday = remainder of dividing Age in months by 12

Data Limitations and Analytical Considerations

When the birth month and diagnosis month are the same, our estimate of age in months at diagnosis is as accurate as if day information were used in the calculation. However, when the months differ, our calculation is not accurate. For example, for a person with a January birth month and a February diagnosis month, the calculated months since last birthday would be one month. But in reality, it could be anywhere from 1 day to 59 days (assuming 30 days in every month). Therefore, in any calculated month after last birthday, about 50% of patients are in fact one month younger (assuming equal distribution of patients by birth month and diagnosis month). In aggregate, the number of patients with zero month is underestimated by 50% and the number of patients with 11 months is overestimated by 50%. Caution should be exercised in using this variable, given the limitation.

How to Access the Calculated Months Fields Database

In order to access a specialized database, you must already have access to the latest SEER Research Plus Data.

  • If you do not have access to the latest SEER Research Plus Data, first follow the steps on How to Access the SEER Data.
  • If you already have access, send an email to to request access to the Calculated Months Fields Database.
    • Include your SEER*Stat username.
    • Add a brief description of your project and research goals in the email, including the types of analyses or statistics you will use.