----start path.lec.05.05.97----

dr weber...
moving along with the final chart on metastasis.
going from primary neoplasm to metastases
the steps you go through are the steps he went through in class...
what you can do is, from the discussions last time you can put in
vascularization, embolization, loss of adhesive properties, etc etc.

even though most tumors go through progressive growth, and get 
progressive heterogeneity of cells allowing them to have different 
functional capacities, etc...some tumors have all these characteristics 
right from the start. then, the line goes from primary neoplasm right to 
mets, because those other steps occur pretty much right away - tumor has 
all those characteristics from the beginning. but MOST tumors go through 
progressive growth, gradually acquiring different functional capacities.

chemical carcinogens, radiation carcinogenesis.
we already know how these work - these are initiating factors which 
induce neoplasia via point mutations, probably - a whole bunch of point 
mutations. usually this results in activation of p-oncs, loss of 
suppressor genes, etc. but they basically work on those genes somehow.

cc's are very diverse in structure. some are found in nature eg very 
potent cc exists in a fungus - Aspergillus fumigatus, which frequently 
grows on peanuts, grains. makes a potent mutagenic toxin called aflatoxin 
B1 which causes liver cancer. most of the other cc's can actually be 
divided into direct acting or indirect acting ccs. 

that's a good way to remember how they work, b/c direct acting cc's 
usually alkylating agents, many of them are used in chemotherapy eg 
cyclophosphamide or busulfan, chlorambucil - these compounds inhibit DNA 
synthesis, killing the cell - but when the are accumulated in the right 
amount, cells will actually survive but will have mutations. so if animal 
is treated with these drugs, you may be able to cure the existing 
neoplasm, and wipe out all the cancer cells, because these drugs attack 
cells that are actively in the cell cycle, but the rest of the body 
survives, and now you have cells with mutations in them, so the patient 
may get a secondary neoplasm esp leukemia years down the line.

these compounds do not need metabolic activation. they act directly.

now, the INDIRECT ccs are often called "procarcinogens" and they DO need 
to be metabolically activated. then, it becomes the "ultimate carcinogen" 
that actually induces the mutation in the DNA. of these indirect cc's, 
the group most important to recall is most of the polycyclic 
hydrocarbons, eg benzpyrene, methylchalanthene (?). benzpyrene is in 
cigarette smoke.

these are normally metabolized by the liver, and often, the liver 
actually inactivates it, and the enzymes that do this are the "mixed 
function oxygenases" aka p450 et al. these enzymes are along the ER and 
they normally inactivate these materials. they then conjugate them with 
glucoronic acid and they are excreted. BUT in many instances, they 
produce EPOXIDES - very electrophilic compounds, e- deficient molecules, 
so they want to interact with e- rich molecules, which are found in DNA 
and RNA. the enzymes responsible for this vary with species and tissue. 
if you take the methylcholanthene and induce neoplasia on mouse skin, it 
doesn't follow that you can induce neoplasia on cat skin with same 
chemical - cat m ight not have the right enzyme in the skin.

but the liver contains many of these enzymes in many species. 

remember: latent period, between exposure and development of neoplasm, 
can be years. also, these ccs, whether direct or indirect, can also work 
together with radiation or viral induced mutations. this is just ONE way 
of producing point mutations, whereas radiation can work in concert with 
them...

with cc's, PROMOTING AGENTS are also important. promoting agents differ 
from initiating agents (cc's). a promoting agent is anythign that can 
induce mitosis in the initiated cell. so, a chronic viral or bacterial 
infxn that kills cells in the body will automatically lead to some 
regeneration in the affected tissue. if an initiator has already been 
there...

so simple induction of mitosis can drive a cell, previously transformed 
by an initiator, to go into mitosis, and after several cycles, the cell 
is "fixed" transformed and will go on to neoplasm

trauma is also a promotor - it causes cell death, and regeneration. eg 
skin -if you put methylcholanthene, put it on mouse ear, then repeatedly 
traumatize ear skin, tumor will develop along the border of the trauma.

there are a number of other normal substances that promote...hormones. 
many body tissues are regulated in terms of growth cycles with hormones 
via receptor mechanisms. these tissues are under influence of hormones 
all the time. natural hormonal cycles can turn these cells into 
transformed cells. 

more potent ones: phorbol esters, actually found in croton oil. this is 
an oil prepared from a plant. this oil was used in research. it's a 
highly irritating oil. the skin was initiated with methylcholanthene, 
then painted with this oil. it turns out these phorbol esters impinge on 
protein kinase C - cell starts phosphorylating proteins constantly, 
turning on cell, inducing mitosis.

mutations are cumulative. more you get exposed, more additional random 
point mutations can occur. point mutations always translate to either 
activation of p-onc or loss of suppressor gene, when we're talking about 
induction of neoplasia. usually you need several such mutations to induce 
neoplasia.

carcinogen-->metabolic activation-->epoxides-->binding to DNA, adduct 
formation-->permanent DNA lesion, initiated cell----> cell proliferation, 
altered differentiation--->neoplasia


OR

carcinogen--->detoxification--->excretion
...epoxide--->detoxification--->excretion
....binding to DNA-->DNA repair-->normal cell
....binding to DNA--->cell death

initiation = everything up to and including Permanent DNA lesion
promotion = cell proliferation, altered differentiation, transformation 
to neoplasm.

experimental induction of neoplasia:

polycyclic hydrocarbon is put on skin [x], then a promotor is applied at 
varying intervals [o].

x ______________________________________NO TUMOR
xoooooooooooo___________________________TUMORS
x__________oooooooooo___________________TUMORS
oooooooooox_____________________________NO TUMOR
oooooooooo______________________________NO TUMOR
x__o__o__o__o__o__o__o__o__o__o__o__o___NO TUMOR

|--------time--->-----------------------|

note that if application of promotor occurs at intervals too far apart, 
cell is able to repair damage before permanent transformation occurs.

so. if someone smokes all the time, not only are they inducing mutations, 
but they are ALSO applying a promotor constantly. so this is a perfect 
setup for cancer to develop - constant application of initiators and 
promotors...

[STOP SMOKING!! DON"T DO IT!! SPEND SOME TIME ON A LUNG CANCER WARD OR 
WATCH A LOVED ONE DIE SLOWLY AND PAINFULLY OF LUNG CANCER - I DID...TRUST 
ME, YOU WILL NEVER SMOKE AGAIN!]

now. even if you apply same cc in same animal in two different tissues, 
tumor cells will end up with different surface antigens. 

if you induce a tumor on skin with a cc, and then induce a gastric CA 
with same cc in same animal, you end up with tumor cells with different 
surface Ag, so any immune response won't work against both tumors. 
because the cc when it induces mutations, causes the cell to make a new 
protein, but a different one in each transformed cell. a cc isn't 
producing the same mutation each time!

most other kinds of neoplasms do not make good cell surface Ag...eg, 
"spontaneous tumors" - those are poorly antigenic, in marked contrast to 
tumors produced by a specific cc in a very potent dose. this is why its 
so hard to get immune system to fight these suckers off.

if you induce tumor in same animal with same cc in same tissue in two 
different locations, you will still have different tumor surface 
antigens.

metastatic tumors will have the same antigens as the primary tumor up to 
a point. but as tumor grows, it could lose or modulate its antigenicity, 
so mets may have less antigenicity than the primary tumor.

a couple of minor things.
radiation induced tumors: can have point mutations, or more drasticly 
chromosomal translocations, etc. with these tumors, you have to consider 
the dose, the dose rate, the mitotic cycle of the tissue exposed. 
radiation is more able to induce tumor in tissue already undergoing a lot 
of mitosis - eg skin, GI tract, bone marrow. eg, leukemia.

total dose: 800 R = fairly high dose.
dose RATE: 2 r/min = low dose rate. compare to 200 r/min = high dose rate


eg, if dr weber hits you on the head 1/hr, that's low rate. if he hits 
you on the head 100/hr, that's a high rate.

so at the low rate, you're being exposed for 6 hrs and 40 min. at the 
high rate, you're being exposed for 4 minutes. which is more of a 
problem? a high dose at low rate or high rate? well, the high dose rate 
causes so much gross chromosomal fragmentation that in essence, the cell 
is nonviable. it won't be able to divide. you can't get two viable 
daughter cells. the daughter cells will die. this is the "therapeutic 
effect" - you get a lot of mutations, but you can't cause a tumor b/c the 
daughter cells all die. at the low dose rate, you have mutations, and 
there is no gross chromosomal damage, so you CAN produce daughter 
cells...so that's more dangerous.

so when people have radiation therapy, sometimes they get secondary 
tumors. usually the therapy is at very high dose rates, so why do you 
sometimes get a secondary neoplasm? well, at the edge there is some 
scatter. some cells will get radiation damage but remain viable. these 
cells can develop into a secondary neoplasia.

in contrast to antigenicity of cc induced tumors, which are always 
different...when you have a tumor induced by oncogenic virus, regardless 
of what tissue the virus initiates - eg, fibroblasts, or epi, or whatever 
- the antigens on tumor surface are identical for all tumors induced by 
that virus. that's because the virus codes for the surface Ag. so for 
these, you could potentially vaccinate against these, and that is done.  
but only a handful of viruses induce tumors that we know of.

----break----

[slides]
mets:
seeding
lymphatic spread

old female dog, just caudal to elbow is irregularly defined multinodular 
fungating mass in sq tissue w/surface ulceration and yellow area of 
necrosis. a number of nodular formations in regional skin. anterior to 
scapula, lesions present grossly similar to other lesion. are these all 
related? what could it be? which is primary? the large ulcerated mass is 
probably primary, but we're not 100% sure. but it's bigger, and more 
developed. what kind of tumor could this be? mammary adenocarcinoma, 
squamous cell carcinoma; unlikely to be fibrosarcoma, which usually forms 
a larger tissue mass and grows deep, whereas scc tends to fungate. 

retrograde spread: tumor cells grow from the primary area, and extend in 
the lymphatics (like moss in river bed), and then make secondary nodules 
in another area. so in this dog, we'd want to look at axillary and 
prescapular LNs.

LN: one germinal center seen  which appears normal. above it is an 
epithelial/glandular looking tissue mass which clearly doesn't belong 
here.

SEEDING: mets via seeding...parietal pleura, thoracic cavity...the 
ventral 1/3 of pleura is covered w/individually discrete and coalescing 
pink to pink-grey smooth surfaced nodules on a hyperemic or hemorrhagic 
parietal pleura. this is a tumor growing by seeding. it's a mesothelioma 
which orignates on mesothelium (which covers parietal pleura). the 
original tumor sheds tumor cells into pleural cavity, which land on other 
sites and grow into new tumors.

urogenital tract..there is a considerable amount of destruction of normal 
architechture of urethra, as well as multiple coalescing masses within 
the bladder, which appear similar to the tissue which has taken over the 
urethra. this appears to be a malignancy - borders are poorly defined. 
this tumor probably originated in urethra.

remember: most likely means of metastasis of a carcinoma is via 
lymphatics. but if you are located within a lumen eg bladder, thorax, 
peritoneum - you could also have seeding.

manibular area: very large LNs. smooth, encapsulated - this is 
lymphadenopathy. pathological involvement of the LNs. well, so far, we 
don't know why. could be hyperplasia, chronic inflammatory response, 
granulomatous rxn, could be neoplasia.
cutting into the LN reveals a uniformly grey, bulging tissue mass w/no 
normal architecture. another LN is similar with patchy areas of 
hemorrhage. the spleen is enlarged and completely covered with 
multifocal/coalescing pale pink areas interdigitating with the normal 
dark red tissue. probably that is white pulp - lymphoid tissue. spleen so 
full of proliferating cells probably not as much blood flowing through 
it. this looks like lyphosarcoma.

can see involvement of any organ system. diffuse infiltration of 
myocardial tissue by same kind of cells in LN can occur...heart appears 
to be "fat covered" but it's not really fat. inside, the myocardium looks 
very pale, swollen, hemorrhages exist (petechia). metastatic 
lymphosarcoma. 

remember most lymphoid tumors are B cell tumors.

lymphocytic leukemia: need to know if BM is totally occupied by lymphoid 
cells, and if there is huge number of circulating lymphoblasts in 
peripheral blood.

lymphosarcoma: doesn't have the above. but you can have "lymphosarcoma 
with leukemic blood picture". you do have accumulation/infiltration of 
malignant lymphoblasts in various organs.

this confuses me.

if organ is pale, enlarged, rounded, with uniform-diffuse involvment, 
could be lympho.

spleen commonly HUGE with lymphosarcoma. on sectioned surface, there is 
bulging grey-pink tissue mass. very rounded edges. today we will look at 
an enlarged spleen in lab. consider what else can make a spleen large.

what can induce splenomegaly? many things..
lymphoid tumors do not induce a lot of stroma formation. these tumors 
grow by expansion. not a lot of angiogenesis or fibroplasia occurs. from 
dx standpoint, this is interesting. if you cut an LN or spleen, you can 
scrape off huge # of cells, put them on slide and stain them and make a 
dx. that's b/c they make such a small amt of stroma. 
histologically, lymphosarcoma looks like free floating tumor cells. no 
vessels, no collagen, etc. or very little. in large tumors, may see areas 
of necrosis as well.

young cat with huge mediastinal mass and bulging grey tissue mass sitting 
in mediastinum and similar tissue encasing the heart. this is probably 
lymphosarcoma. thymic lymphosarcoma, involving T cells. usually occurs in 
cats under 3 yrs old. etiologic agent is probably FeLV - an RNA 
retrovirus that probably induces transformation through insertional 
mutagenesis. it isn't a rapidly transforming virus. 

12 yr old cat with heart covered by huge tissue mass...in an old animal, 
there's another tissue that can involve the thymus and also produce a 
neoplasm. you could have a thymoma of the epithelial component (thymus 
has those corpuscles,remember?). a tumor of epithelial type in the thymus 
is called a THYMOMA. thymic lymphosarcoma happens in young animals; 
thymoma in older ones. thymoma is firmer, has more stroma, is tumor of 
epi cells, not lymphoid cells (t cells). THYMOMA is usually locally 
expansive, can locally infiltrate, does not metastasize. 

---end----