JUSTIN F GAINOR MD
NPI 1487813010
Internal Medicine - Medical Oncology in Boston, MA
About Justin F Gainor Md NPPES
Official registry information on file with the National Plan and Provider Enumeration System.
JUSTIN F GAINOR MD (NPI 1487813010) is an individual medical oncology provider in Boston, Massachusetts, licensed in Massachusetts (245561) and active in the NPI registry since June 2008. He is enrolled in Medicare PECOS, is affiliated with North Shore Medical Center -, and maintains 2 additional practice locations.
NPPES Registry Identity
Specialties & Licenses 3
Secondary Practice Locations 2
Accepted Insurance
Medicare Participation & PECOS CMS
Medicare enrollment, assignment, billing reassignment, and ordering and referring status from CMS.
Medicare Enrollment Status
Enrolled in Medicare and accepts Medicare assignment
Justin F Gainor Md is registered in PECOS and agrees to accept the Medicare-approved amount as full payment. Medicare patients are not billed beyond the standard deductible and coinsurance.
Medicare Billing Reassignments
3Medicare enrollment records show Justin Gainor reassigns Medicare billing to 3 organizations. Each organization bills Medicare for the services this provider delivers there; the nearest is listed first.
Boston, MA 02115
- Reassigned Medicare billing, Massachusetts enrollment
- 4,574 clinicians in this Medicare group
Boston, MA 02114
- Reassigned Medicare billing, Massachusetts enrollment
- 6,234 clinicians in this Medicare group
Boston, MA 02114
- Reassigned Medicare billing, Massachusetts enrollment
- 6,360 clinicians in this Medicare group
Source: CMS Revalidation Reassignment List, October 2026 release. Reassignment records can lag staffing changes; confirm a current affiliation with the organization.
Areas of Expertise CMS Part B claims 8
Services this provider delivered to Medicare fee-for-service patients, from the CMS Medicare utilization data. Higher counts generally reflect more experience with a service; care delivered outside Medicare is not included.
Hospital Affiliations CMS Care Compare 5
Hospitals where this provider delivers care, identified from recent Medicare claims and place-of-service records.
North Shore Medical Center -
Acute Care Hospitals · Salem, MAMassachusetts General Hospital
Acute Care Hospitals · Boston, MANewton-Wellesley Hospital
Acute Care Hospitals · Newton, MABrigham And Women's Hospital
Acute Care Hospitals · Boston, MAFaulkner Hospital-Brigham And Women's
Acute Care Hospitals · Boston, MAPhysician Visit Costs CMS claims · ZIP area
Typical Medicare office-visit costs in the 02114 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.
Other Providers at the Same Location NPPES 20
Providers registered at the same practice address, or within the immediate area, according to the NPPES registry.
BOSTON, MA 02114
BOSTON, MA 02114
BOSTON, MA 02114
BOSTON, MA 02114
BOSTON, MA 02114
BOSTON, MA 02114
Frequently Asked Questions NPPES & CMS
Common questions about this NPI record, answered from the official NPPES registry and CMS datasets shown on this page.
What is Justin Gainor's NPI number?
The NPI number for Justin Gainor is 1487813010. It was assigned to this individual provider in the NPPES registry on June 9, 2008.
Where is Justin Gainor located?
Justin Gainor practices at Massachusetts General Hospital 55 Fruit Street, Boston, MA 02114. The listed phone number is (617) 726-2862.
What is Justin Gainor's specialty?
The primary specialty registered for this NPI is Internal Medicine, specializing in Medical Oncology, with taxonomy code 207RX0202X.
Is Justin Gainor enrolled in Medicare?
Yes. Justin Gainor is registered in the Medicare PECOS system and accepts Medicare assignment, which means accepting the Medicare-approved amount as payment in full for covered services.
Which organizations bill Medicare for Justin Gainor's services?
According to the CMS Revalidation Reassignment List (October 2026 release), Justin Gainor reassigns Medicare benefits to 3 organizations: Brigham & Womens Physicians Organization Inc (Boston, MA), The General Hospital Corporation (Boston, MA) and Massachusetts General Physicians Organization Inc (Boston, MA). Each reassignment is filed with Medicare on form CMS-855R, signed by both the clinician and the organization, and lets the organization bill Medicare and receive payment for Justin Gainor's services. Reassignment records can lag staffing changes; confirm current arrangements with the organization.
What insurance does Justin Gainor accept?
Health plans from Taro Health list Justin Gainor as in-network in at least one marketplace plan. Coverage varies by plan and year; verify with the insurer or the provider before a visit.
Is Justin Gainor affiliated with any hospitals?
According to CMS data, Justin Gainor is affiliated with North Shore Medical Center -, Massachusetts General Hospital, Newton-Wellesley Hospital, Brigham And Women's Hospital and Faulkner Hospital-Brigham And Women's.
When was this NPI record last updated?
The NPPES record for Justin Gainor was last updated on August 11, 2026. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 2 months ago. If this record has changed at CMS more recently, you can request an on-demand re-check against the live CMS registry, directly from this page.
# Justin F Gainor, MD · NPI 1487813010
Medical Oncology physician in Boston, Massachusetts. Individual provider, active in the CMS NPPES registry since June 9, 2008.
## Identity
- **NPI:** 1487813010 (Entity type: Individual)
- **Enumerated:** June 9, 2008
- **Primary specialty:** Internal Medicine - Medical Oncology · taxonomy 207RX0202X
- **State license:** 245561 (Massachusetts)
- **Sole proprietor:** No
## Practice location
- **Address:** MASSACHUSETTS GENERAL HOSPITAL, 55 FRUIT STREET, Boston, MA 02114
- **Phone:** (617) 726-2862
## Medicare
- **Medicare:** Enrolled (PECOS); accepts Medicare assignment
- **Ordering & referring:** eligible for Part B labs & imaging, durable medical equipment, home health, power mobility devices
- **Bills Medicare through:** 3 organizations under Medicare reassignment (form CMS-855R): Brigham & Womens Physicians Organization Inc (NPI 1033535497, Boston, MA); The General Hospital Corporation (NPI 1023049236, Boston, MA); Massachusetts General Physicians Organization Inc (NPI 1801874573, Boston, MA) · CMS Revalidation Reassignment List, October 2026 release
- **Medical school:** Harvard Medical School, class of 2008
## Record status
- **NPPES last updated:** August 11, 2026
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Source: [NPI Profile](https://npiprofile.com/npi/1487813010) · Data from the CMS NPPES public registry.