History of Bone Tumor Pathology
Moderators: K. Krishnan Unni and Franco Bertoni
Section 5 -
History of Bone Tumor Pathology
The history of bone tumor pathology at Mayo Clinic is synonymous with the personal history of Dr. David
C. Dahlin. However, Dave would be the first to mention the influence of others on the development of the
discipline at Mayo Clinic. All of pathology at Mayo Clinic traces its origin to the arrival of Dr. L.
B. Wilson to Rochester, Minnesota on January 1, 1905. Dr. Wilson had been recruited from the University
of Minnesota to join the Mayo brothers in their practice. Drs. Will and Charlie Mayo both recognized
the importance of being able to accurately diagnose the patient's condition while he/she was still on the
operating table. They realized this would allow them to alter their surgical approach to best meet the
patient's needs. The primary value of Mayo Clinic is "The needs of the patient come first" and with the
recruitment of a pathologist the Mayo brothers realized that they would better meet both theirs and the
Dr. Wilson immediately went to work on solving the problem which the Mayo brothers had posed to him -
the need to have a technique which would allow for rapid histologic evaluation of specimens obtain at
surgery. The solution perfected was the frozen section and therefore Dr. Wilson is arguably the
"father" of the frozen section evaluation and intra-operative consultation. The technique which Dr.
Wilson developed continues to be used today at Mayo Clinic over 100 years latter.
Dr. Wilson's efforts in the development and perfection of the intraoperative evaluation of pathologic
specimens was to have a profound effect on medicine as well as on individual physicians. Dr. Dahlin was
an individual who was profoundly influenced. Dr. Dahlin was grew up in a small town in South Dakota
(Centerville). He attended college at the University of South Dakota and like many from the Dakota's
completed his medical education at Rush Medical School in Chicago. Having completed his medical
education in Chicago he entered a rotating internship program at Anker Hospital in St. Paul, Minnesota.
In order to enter the training program he had to sign a contract. He once told me that the contract
specifically stated that he would receive "twelve equal payments of zero dollars per month for a period
of twelve months." Like many of his generation Dr. Dahlin had aspired to be a surgeon and he had been
accepted into the surgical residency at Mayo Clinic. World War II intervened and he before he could
enter residency he was drafted into the Army Medical Corps. Upon his return from service he entered the
Mayo Graduate School of Medicine and his first rotation was in Surgical Pathology at St. Mary's
Hospital. He came under the influence of Dr. Malcolm Dockerty who was a senior surgical pathologist
using the technique for intraoperative diagnosis described by Dr. Wilson. Dr. Dahlin was captivated by
both Dr. Dockerty's enthusiasm and for the potential to positively influence the operative care of
patients. He switched his residency to pathology and completed the training program in 1948.
Dr. Dahlin quickly developed an interest in Orthopedic pathology. Having trained in Chicago he was
aware of Dr. Dallas Phemister who was Chair of Orthopedics at the University of Chicago. Dr. Phemister
had maintained a collection of cases, including pathology, which became known as the "Phemister
Collection." Dr. Phemister pioneered the use of autografts to reconstruct segmental bone defects for
extremity tumors and the resection of these tumors was the basis of the collection . By 1950 Dr.
Dahlin had co-published an article on "Eosinophilic Granuloma of Bone"  with an orthopedic surgeon and
a radiologist. Thus, early in his career, Dr. Dahlin established the pattern of
clinical-radiographic-pathologic correlation which would define his professional life. Having spent time
reviewing the "Phemister Collection" Dr. Dahlin returned to Rochester with renewed enthusiasm for
orthopedic pathology. Some of the orthopedic surgeons at Mayo Clinic had developed an interest in bone
tumors and he realized that in order to appropriately treat patients with these conditions that specific
pathologic diagnosis was required. By 1952 Dr. Dahlin had collaborated with Dr. Ivins on the
publication of a study of "Primary Reticulum-cell Sarcoma of Bone."  The excellent medical records
(the "unified" medical record introduced by Dr. Henry Plummer soon after Dr. Wilson joined the Mayo
brothers) at Mayo Clinic afforded Dr. Dahlin and his colleagues an opportunity to study orthopedic
tumors in a unique manner. Follow-up information was easily obtainable through the unified record which
gave these individuals an opportunity to identify trends and outcomes that were difficult to appreciate
Dr. Dahlin created a database of information on all of the patients with bone tumors seen at the Mayo
Clinic and on all of the cases he saw in consultation. This database was not electronic but was
efficiently maintained on 4X6 index cards which were filed in order of the patients unique Mayo Clinic
identification number or by date of accession of the consultation case. The information on these index
cards was also recorded in a three ring binder by diagnosis. In this way he created a "relational
database" which would become the source of information for numerous clinical-pathologic studies.
By 1957 Dr. Dahlin had published the first edition of his book on bone tumors and tumor-like conditions.
This text became a standard reference for orthopedic pathologists as it succinctly summarized the
clinical, radiographic and pathologic features of bone tumors and tumor-like conditions. The focus on
the long term follow-up of patients captured on those 4X6 cards allowed Dr. Dahlin to identify the
"hazards of radiation therapy for giant cell tumor of bone" as early as 1957.  The publication of his
book and the many articles he authored/co-authored utilizing the long term follow-up available through
the Mayo Clinic unified medical record and his consultation files led to visiting professorships and
lectures around the world.
Dr. Dahlin was willing to share his thoughts, opinions and diagnosis with anyone and was not intimidated
by the possibility that he could be wrong. His love of the intra-operative consultation had been
fostered by Dr. Malcolm Dockerty who lived his professional life by the dictum "Errara Raro Num Quam
Dubitare" (loosely translated, seldom wrong, never in doubt). Because he was willing to share the
thought process he used to arrive at a diagnosis he was recognized early in his career as a gifted
educator. The South Bay Pathology Society (California) invited the young Dahlin to lecture the group in
1961. As recorded in the early history of that society  Dr. Dahlin was willing to review slides and
clinical history in a forum including orthopedic surgeons. "This format met with considerable
enthusiasm, and this generated the idea of charging a registration fee to be used to invite Dr. Dahlin
to come out to California to present the pathology findings."  Thus early in his career David Dahlin
established a tradition of open discussion of difficult cases and a willingness to put his diagnostic
reputation on the line.
During the course of his career at Mayo Clinic Dr. Dahlin trained many young colleagues in general
pathology. However his enthusiasm for orthopedic pathology was infectious and the majority of young
pathologists training at Mayo Clinic had at least one paper co-authored with him before completing their
training. No young pathologist was more influenced by Dahlin than Dr. K. K. Unni. Like Dr. Dahlin,
Dr. Unni had originally started his post-graduate education thinking that he would be a surgeon. When
Kris decided that pathology was the field he was most attracted to he spent time in training in Wooster,
Massachusetts. His mentors there realized that he was destined to be a great pathologist and suggested
that he seek training at Mayo Clinic. Not surprisingly Dr. Dahlin recognized Kris's talents and
mentored him during his residency and early post-residency career. The relationship between Drs. Dahlin
and Unni became one of deep respect and affection. They co-authored subsequent editions of the text
Dahlin had originally published and shared difficult orthopedic pathology cases until Dr. Dahlin died in
The close working relationship between pathologists, radiologist and orthopedic surgeons which Dr.
Dahlin had recognized as central to good patient care resulted in a weekly conference at Mayo Clinic.
Cases seen and treated in the previous week were discussed openly and used as "teaching cases" for both
the young and the old members of the staff. Through this Thursday morning seminar generations of young
radiologists, orthopedic surgeons and pathologists were introduced to the subtleties of orthopedic
pathology. Drs. Dahlin and Unni trained numerous young pathologists in this forum. Not only were
residents and fellows who had sought training at Mayo Clinic so educated, but also individuals who came
from abroad to spend time in Rochester were similarly exposed to and learned orthopedic pathology. By
spending time in Rochester at the Mayo Clinic pathologist from Asia, Europe, South and North America
learned orthopedic pathology at the "feet" of both Dr. Dahlin and Dr. Unni.
The history of bone tumor pathology at Mayo Clinic is a rich one. It is the story of young pathologist
traveling from around the world to learn together with their colleagues in radiology and orthopedic
surgery. Dr. Dahlin made the journey from South Dakota, Dr. Unni made the journey from India, Dr.
Bertoni made the journey from Italy, Dr. Kim made the journey from Korea and many others made the
journey from elsewhere. Mayo Clinic has focused on the needs of the patient first and physicians have
traveled from around the world to share in the joy of serving those patients. The team approach to the
delivery of care for those patients is exemplified by the history of bone tumor pathology at Mayo Clinic.
- Eosinophilic Granuloma of Bone. Proceedings of the Staff Meetings of the Mayo Clinic, 1950, 25:534-541.
- Primary Reticulum-cell Sarcoma of Bone. Cancer, 1952, 5:1182-1192.
- Hazard of Radiation Therapy for Giant Cell Tumor of Bone. Societe Internationale de Chirugie Orthopedique Congres International de Chirugie Orthopedique Proces-Verbaux, Discussions Et Communications Particulieres 1957, 7:710-713