1. The Mouse as a Model
for Breast Development
and
Breast Cancer
Research
Dr. Tiffany Seagroves
Laboratory of Dr. Johnson
tseagrov@ biomail.ucsd.edu

2. I. BREAST CANCER
INTRODUCTION
Statistics
Risk Factors
Hormones

3. Breast Cancer Statistics
• The lifetime probability of being diagnosed
with breast cancer for American women is 1
in 8 ( NCI, SEER, 1997 )
AGE IS the MOST
IMPORTANT RISK FACTOR
Median Age of Diagnosis is
Between 60-65 (NIH, 2000)

5. Recent Decrease in UK and USA Breast Cancer
Mortality at Ages 50-69 Years
PETO et al. LANCET 355:1822, 2000

6. Breast Cancer Statistics, cont.
(Y-me National Breast Cancer Foundtaion; www.y-me.org)
• Most common form of cancer in women,
excluding skin cancer
• Leading overall cause of death between
women of age 40-55
• ACS estimates that 192,000 American
women will be diagnosed with breast cancer
this year and approximately 46,000 women
will die
• There are more than 2,000,000 breast cancer
survivors in the U.S. today

7. Factors Associated with an
Increased Risk of Breast Cancer
[Love et al. 1996]
• Age of menarche, first child, onset menopause
• Diet, level of exercise, obesity, alcohol consumption
• Presence of benign breast disease (DCIS)
• Exposure to radiation
• Family history and genetics (estimated 5% of total
cases can be contributed to genetic factors, and
20-30% cases can be linked to a family history of
breast cancer)

8. Increase
in
Diganosis
of
Early-
Stage
Breast
Tumors
Since the
1980s

10. 70% of breast cancers occur
in women who have no
identifiable risk factors.
This is why you are supposed to examine
yourself and have yearly exams.

11. Factors Associated with a Significant
Decreased Risk of Breast Cancer (~
30-50%)
• Completed Pregnancy by Age 20
– Exposure to “pregnancy” hormones is protective if
happens early
• Removal of Both Ovaries by Age 35
– Over time, exposure to “pregnancy” hormones
increases risk because ~50% of breast tumors are
initially hormone-dependent

12. Paradox of Hormone
Function in the Breast:
Why do the same
hormones that promote
normal development of the
breast (to prepare for
lactation) act to promote
breast cancers later in
life?

13. The Role of “Pregnancy Hormones”
in Breast Development and
Lactation
1) ESTROGEN AND PROGESTERONE (E+P):
Produced by corpeus luteum of ovary first 6 wks or
pregnancy, then taken over by placenta.
Together, E+P stimulates growth and development of
secretory units and ducts in the gland.
2) PROLACTIN (Prl):
Produced by anterior pituitary
Stimulates production of milk

14. II. ANATOMY AND
HISTOLOGY OF THE
HUMAN BREAST
Whole gland
TDLU unit
Whole mount and H&E staining

15. Source: http://mammary.nih.gov

16. Slice of a Whole Human
Breast
skin
Fatty tissue
Brown area= “epithelium”

17. Acinar 15-yr The Structural
organization female
Units (Terminal
Ductal Lobular
Units, TDLU) of
22 yr nulli-
parous
30 yr nulli-parous the Human
Breast
55 yr parous in 80 yr
menopause parous
Taken from Cardiif and
Wellings, 1999

18. Human TDLU Whole Mount
extralobular terminal ducts
acini
duct
lobules
Cardiff website

19. TDLU Histology: H&E

20. III. ANATOMY AND
HISTOLOGY OF THE
MOUSE MAMMARY
GLAND
Whole Mount
H&E
Comparative Histology with Human

21. The Terminal End Bud of the
Mouse Mammary Gland
TEBs are highly
proliferative
units
that form the
ductal
network

22. Stages of Mouse Mammary
Development: Whole mounts
Alveoli
Duct
www.mammary.nih.gov

23. A-B. 6-P, “early”
C-D. 10-P, “mid”
E-F. 15-P, “mid-to-late”
G. Lactation
H. 4 days regression

24. Which is mouse, which is human?
(row A vs row B?)
A
B
Wellings and Cardiff, 1999

25. IV. WHY THE MOUSE
MAMMARY GLAND IS A
POWERFUL GENETIC
TOOL
Reasons
Experiment approaches
How to make a transgenic mouse
to study development/cancer

26. Why Use the Mouse as a Model for
Breast Cancer?
• Histology is comparable to human
• Can use genetics to manipulate the
mammary glands
• Have multiple pairs of mammary glands that
allow for multiple biopsies
• Can purify epithelial cells from the fat and
culture them

27. Mice have 10 Mammary Glands

28. How to Biopsy a Mouse Mammary
Gland
QuickTimeª and a
decompressor
are needed to see this picture.
QuickTimeª and a
decompressor
are needed to see this picture.

29. Mammary Gland Transplantation
Remove endogenous
epithelium
from stromal fat pad
Transplant a fragment of
tissue
Containing epithelium from
a
donor OR inject purified
cells
Transplanted epithelium grows out
Into fat pad in 6-8 weeks

30. How To Make a Mammary-Gland
Specific Transgenic Mouse
milk protein gene
minimal promoter Your Favorite cDNA
usually MMTV or WAP
Inject into isolated mouse nucleus
Check mammary gland of
female progeny for increased
expression of your gene

31. V. WHAT DO MICE HAVE
TO DO WITH BREAST
CANCER?
Differences between breast and
mouse mammary tumors
How to get mice to develop tumors

32. General Differences Between Human
Breast and Mouse Mammary Tumors
SIMILARITIES DIFFERENCES
• Molecular lesions causing • Most tumors mouse
breast cancer in human have
proven to cause breast cancer metastasize to the lung.
in mice Most human metastasize to
• Similar morphological the regional lymph nodes.
patterns of lesions appear in • Mouse tumors have much
both species
less fibrosis and
• Development of cancer
consistent with multi-hit inflammation
kinetics • *Half of human breast
• Breast cancers in both species cancers are hormone-
are metastatic dependent. Most mouse
• Breast cancers may be tumors are hormone
hormone- independent
independent*
Taken from Thompson and Cardiff

33. How to Cause a Mammary Tumor in a
Mouse
• Treat young mice (time most susceptible) with a
chemical carcinogen
• Make a transgenic mouse that overexpresses a gene
product that regulates growth
• Make a “knockout” mouse that deletes a gene that is
a tumor suppressor
• Breed them several times and watch for spontaneous
tumors (rare in mice, more common in rats)

34. VI. HUMAN BREAST
PATHOLOGY
Examples of Benign Diseases
Tumor Grades/Types
Hyperplasia vs Carcinoma

35. How do pathologists classify and
grade breast tumors?
Benign vs. hyperplastic vs. carcinoma
Well- vs. poorly-differentiated
Nuclear morphology- uniform or not
Degree of proliferation
Ductal or lobular in origin?

36. Wheel of Prognosis

37. What factors predict outcome of
treatment?
• SIZE-the larger the size, fewer patients survive
If <2 cm, 11% lymph-node negative patients will have recurrence in 5
yr; >5cm, 25-30% patients will relapse
• HISTOLOGIC GRADE-higher the grade, less chance for
survival
• ER STATUS-loss of estrogen receptor tends to be negatively
associated with outcome.In particular women with ER-
negative tumors are no longer responsive to
tamoxifen, a widely used adjuvant therapy
• PROLIFERATIVE RATE -low rate proliferation, increased
chances of survival. This factor is also independent of other factors.
• Amplification of certain growth factors or receptors or
loss of certain tumor suppressors (p53)-lead to decreased
survival

38. Benign Breast Disease
1) Fibroadenoma-overgrowth of stroma
Most common benign tumor of the breast; typically occurs in the 20s-30s
2) Cysts-fluid filled
epithelium
may make breasts feel
“lumpy”

39. Human Breast Hyperplasias
Hyperplasia: Any increase in cell number without cytologic
changes in cellular morphology
MILD SEVERE
high
low power power
Atypical Hyperplasia: Any increase in cell number WITH cytologic
changes in cellular morphology, especially nuclear morphology
fine needle
aspiration
low power
note different staining
intensity of nuclei
BUT
cells still attached to
each other

40. DCIS (ductal carcinoma in situ):
the “precursor” to breast cancer
It is in situ or “in place” because the cells are still bound by the
extracellular matrix
Solid
Cribiform
Papillary

41. Breast Carcinomas
the tumor is invading the breast, it has broken through the matrix
Well-differentiated
Abonormal nuclei from
fine needle aspiration of carcinoma
still see glandular
structures resembling acini
Poorly-differentiated
arrows point to nuclei with
different morphology. Note
also cells no longer attached
mass of cells, no to each other
resemblance to acini

42. Metastasis
• Human tumors tend to spread to regional lymph node
first (why lymph nodes under arm also biopsied with
tumor)
• Then tumors spread to small capillaries of the
vascular network
• Breast tumors tend to metastasize to lung, liver,
brain, bone
Liver mets, (white spots)
• It is more rare for rodent tumor models to exhibit
metastasis, but when observed, are usually restricted
to lung

43. VII. MOUSE MAMMARY
TUMOR PATHOLOGY
Benign Disease
Hyperplastic Alveolar Nodules
Carcinomas
Comparative with Human Tumors

44. Mouse hyperplasia: the HAN

45. HANs and Atypical
Hyperplasias

46. Classification of Mouse Mammary
Carcinomas:
1) From non-Genetically Engineered Mice (GEM)
A. spontaneous tumors
B. tumors as a result of infection of with mouse mammary
tumor virus (MMTV)
F. tumors from chemical carcinogen treatment
2) From GEM, usually transgenic mice
In contrast to non-GEM, several GEM transgenic mouse
models develop tumors with similar pathologies to human breast
tumors and more are described every year.
examples: TGFα, neu, c-src, myc transgenic mice
Classification by Cardiff, 2000

47. Examples of Mouse Carcinomas
neu (erb-2) myc
more solid more glandular
ras ret-1
different ras myc neu
nuclear morphologies
from different genes

48. both MMTV-induced
mouse tumors
left; DCIS, solid form
right; neu transgene
left; schirrhous carcinoma
right; src transgene
left; papillary carcinoma
right; a protein kinase
transgene

49. IX. BACK TO
HORMONES:
HOW DO WE KNOW PREGNANCY CAN BE
PROTECTIVE AGAINST BREAST CANCER?

50. A combination of E+P treatment reduces
chemical carcinogen-induced
tumorigenesis in rodents (Nandi et al. 1995, 1999)

51. REFERENCES
http://mammary.nih.gov
http://pathology.ucdavis.edu/tgmice/firststop.html
http://www.y-me.org
http://www.komen.org
http://www.nci.nih.gov/
THE JOURNAL OF MAMMARY GLAND BIOLOGY AND
NEOPLASIA