The Fate of Circulating Tumor Cells
I. Passage of Cells through Capillaries*
IRVINGZEIDMAN
(Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia 4, Pennsylvania)
SUMMARY
Experiments were done to study the behavior of circulating tumor cells as they
engage the lumen of capillaries. The transplantable Vacarcinoma and Brown-Pearce
carcinoma were used in domestic rabbits. Suspensions of cells were injected into the
mesenteric artery while, simultaneously, microcinematic studies were made in the
region of the arterio-capillary junctions of the mesentery. The majority of the cells
from each tumor passed through the capillaries into the venous circulation. Cells of
the Vt carcinoma were arrested more frequently than those of the Brown-Pearce
carcinoma.
It is concluded that tumor cells can distort to fit the narrow capillary tube and so
pass through the capillary circulation into the veins. An occasional cell appears too
rigid to fit into the capillary tube and is thus arrested. The incidence of permanent
cell arrest varies with the type of tumor used.
This report is one of a series concerning the ear
liest stages in the development of tumor metasta
sis. The first event in the formation of a metastasis
is arrest of the tumor cell embolus in a small vessel
of a distant organ. What happens when a circulat
ing, large tumor cell enters a narrow capillary? Is
arrest of the cell simply a matter of mechanical
misfit? Experiments were designed to answer these
questions. In these experiments, microcinematic
studies were made of circulating tumor cells after
their arrival in the capillary bed.
intestine was withdrawn from the anesthetized
rabbit, and the attached mesentery was placed in a
special chamber freely movable on the micro
scope stage (Fig. 1). A 27-gauge needle with at
tached polyethylene tubing was inserted and fixed
in the mesenteric artery (4). Then a microscopic
search was made for an arterio-capillary junction
in the mesentery. After a suitable site was found,
the tumor suspension was injected into the mesen
teric artery via the polyethylene tube and needle
(Fig. 2). Simultaneously, microcinematic records
were made of the cells arriving in capillaries. After
each microcinematic study, the intestinal loop was
returned to the peritoneal cavity, the abdominal
wound was closed, and the rabbit was saved. All
rabbits were sacrificed 1 month after injection, and
intestinal loops were examined. Tumor was found
in over 95 per cent of the animals, often in the
form of miliary mesenteric nodules distal to the
site of the injected mesenteric artery. Thus, viable
cells were present in the tumor suspensions.
Prior to studies with tumors, splenic cell suspen
sions were injected into the mesenteric artery to
study the behavior of normal leukocytes and histiocytes. These cells are present in tumor suspen
sions and are often differentiated with difficulty
from tumor cells. Thus, a knowledge of the be-
MATERIALS AND METHODS
The transplantable V2 carcinoma and BrownPearce carcinoma were used in domestic rabbits.
Suspensions of tumor cells were prepared by pass
ing fragments of tumor through a sieve into a mix
ture of serum and balanced salt solution. Clumps
were removed from the suspension by centrifugation.
The rabbit's mesentery was the site chosen for
the study of circulating tumor cells. A loop of small
* This investigation was supported by Grants C-2356 and
CRT-5022 from the Division of Research Grants and Fellow
ships of the National Institutes of Health, United States Pub
lic Health Service, and by an Institutional Grant from the
American Cancer Society.
Received for publication June 23, 1960.
88
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Fio. 1.—Slidingmetal plate and chamber to hold loop of
intestine and its mesentery. The circular metal plate is freely
movable on the microscope stage and can be fixed in place,
when necessary, by the perforated metal bars and bolts seen on
the left side of plate. The chamber for the mesentery occupies
the center of the plate and consists of two pieces of sheet plastic
and four perforating screws and bolts. In operation, the mesen
tery is held between the two layers of plastic; saline at 87°C.
separates the mesentery from the plastic sheets.
Fio. 2.—Injection of the mesenteric artery. The needle is
fixed in the mesenteric artery by a fine steel spring mechanism.
The tumor suspension is injected by a syringe through poly
ethylene tubing which is attached to the needle. In all experi
ments, the intestine is covered with gauze soaked in saline at
37°C.; the gauze is omitted from this picture.
FIGS.Sa-c.—Passage of cell from Brown-Pearce carcinoma
through the capillary. Note the marked elongation of the cell as
it squeezes into the narrow capillary lumen. Excerpts from
film, X1500.
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PÃ-os.5<j-c.—Permanent arrest of Vj carcinoma cell at arteriolar capillary junction. Excerpts from beginning and end of
a film lasting 30 minutes. The shape of the cell is relatively
unaltered during the entire course of the experiment. X1500.
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Flos. 4<z-c.—Transcapillary passage of cell from BrovvnPearce carcinoma. In 4a, the cell is in the artery and covers the
origin of the capillary. In 46, note dumbbell shape of cell as en
gagement of the capillary lumen by the cell ensues. 4c shows
artery and capillary after cell has passed through capillary into
a venule. Excerpts from film. X1500.
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FIGS.5o-c.—Permanent arrest of \\ carcinoma cell at arteriolar capillary junction. Fixcerpts from beginning and end of
a film lasting 80 minutes. The shape of the cell is relatively
unaltered during the entire course of the experiment. X1500.
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FIG. 6.—Large Brown-Pearce carcinoma cell about to en
gage the lumen of a capillary. Left arrow points to cell. Two
arrows on right point to boundary of capillary lumen. Note
difference in size of cell and diameter of capillary through
which the cell subsequently passed. Excerpt from film. X1500.
FIG. 7.—Brown-Pearce carcinoma cell entering a capillary.
Two arrows on left point to walls of the capillary. Note dis
parity between size of cell and the lumen of the capillary
through which the cell eventually passed. Excerpt from film.
X1500.
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ZEIDMAN—Fate of Circulating
havior of such non-neoplastic cells at arteriocapillary junctions was an essential preliminary.
In eight experiments with rabbit spleen cells, a
total of 22 histiocytes or leukocytes stopped mo
mentarily at arterio-capillary junctions and then
passed quickly through capillaries into venules.
No cells were arrested permanently. Subsequent
microcinematic studies with tumor cells revealed
that some small cells of the tumor suspension
which passed through capillaries could be, indeed,
inflammatory cells of the tumor stroma. However,
large cells and permanently arrested cells could be
classified as neoplastic cells with reasonable cer
tainty.
RESULTS
Most cells of the V2 carcinoma and BrownPearce carcinoma passed through the capillaries
after momentary arrest at the arterio-capillary
junction (Figs. 3, 4). In total, fourteen experi
ments were completed with each of the rabbit tu
mors. In experiments with the V2 carcinoma, 29
cells stopped at the arterio-capillary junction.
Twenty of these cells then passed through the
capillary into the venule, and nine were arrested
permanently at the arterio-capillary junction or in
the lumen of the capillary nearby. The passage of
cells through capillaries was more striking in ex
periments with the Brown-Pearce carcinoma.
Here, 32 of 33 cells passed through the capillaries,
and only one cell was permanently arrested.
The change in shape of each cell during transcapillary passage was noteworthy (Figs. 3, 4).
After arriving at the arterio-capillary junction, the
cell paused and completely obstructed the capil
lary at its origin. Then the cell elongated into the
lumen of the capillary, thus conforming to the in
terior of the narrow tube. Once conformation oc
curred transcapillary passage of the cell followed
rapidly, and the intracapillary blood flow re
newed.
Since many of the Brown-Pearce cells were very
large (Figs. 6, 7), the marked plasticity of these
cells was evident. The cell distortion coincident to
engagement of the capillary tube was often ex
treme. Some of the ¥2carcinoma cells revealed
similar shape changes on passing through capil
laries. However, a different picture was presented
by those V2 cells destined for permanent arrest
either at arterio-capillary junctions or in the
nearby segment of the capillary. Such cells, after
arriving at arterio-capillary junctions, blocked the
capillaries but did not change shape (Fig. 5). Dur
ing the entire time of observation, the original
shapes of the cells were usually maintained. Per
manent arrest of cells seemed due, at least in part,
to cell rigidity.
Tumor Cells
DISCUSSION
The results of these microcinematic studies per
mit a re-evaluation of the old mechanical concept
that arrest of tumor cell emboli depends on the
disparity of size between the embolus and the ar
resting vessel. In our experiments with single-cell
emboli, the cell size did not appear to be a deter
mining factor in the incidence of permanent arrest.
Many large Brown-Pearce cells elongated to
squeeze through the narrow capillaries. Yet,
smaller V2 cells were arrested at arterio-capillary
junctions. The arrest of cells seemed to depend, at
least in part, on cell rigidity—on the inability of
the cell to elongate in the direction of the long axis
of the capillary lumen.
Cells of the Brown-Pearce and V2 carcinomas
were also used in previous experiments related to
the above work (4). The incidence of immediate
passage of tumor cell emboli through the lungs was
determined. Tumor cells were injected intrave
nously, and the aortic blood was collected simul
taneously. The presence of tumor cells in the
aortic blood indicated immediate transpulmonary
passage. It was found that the cells of the BrownPearce carcinoma passed through the lungs more
frequently than did V2 carcinoma cells. The pres
ent direct microcinematic observations correlated
well with the transpulmonary studies by showing a
comparable difference in incidence of transcapil
lary passage in the rabbit's mesentery.
Transcapillary passage of tumor cell emboli
probably occurs often in man. Tumor cells are
found in the peripheral blood stream of cancer pa
tients (1-3). It is likely that cells arrived in this
peripheral location only after unarrested passage
through the capillary circulations of organs, prob
ably in a fashion similar to that demonstrated by
our microcinematic studies.
ACKNOWLEDGMENTS
The author is indebted to Mr. Spencer Ward and Mrs.
Isabel Shannon for technical assistance, to Mr. William Fore
for photographs, and to Mr. Joseph Devlin for line drawings.
REFERENCES
1. ENGELL,,H. C. Cancer Cells in the Blood. A Five- to NineYear Follow-up Study. Ann. Surg., 149:457-61,1959.
i. MOORE,G. E.; SANDBERO,A.; and SHUBARG,J. R. Clinical
and Experimental Observations on the Occurrence and
Fate of Tumor Cells in the Blood Stream. Ann. Surg., 146:
580-87, 1957.
8. ROBERTS,S. S.; WATNE,A. L.; McGRAin, R. G.; McGREW,
E. A.; ÑAMO»,
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4. ZEEDMAN,
I., and Buss, J. M. Transpulmonary Passage of
Tumor Cell Emboli. Cancer Research, 12:731-33, 1952.
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The Fate of Circulating Tumor Cells: I. Passage of Cells through
Capillaries
Irving Zeidman
Cancer Res 1961;21:38-39.
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