Targeting cancer is not simple as it possess the similar targets as the normal cells have. Therefore selectivity is the major issue whereas the other issues like toxicity and resistance must need to be addressed. But recent up-gradation in cancer biology bring better perspectives especially in case of understanding the behavior of a cancer cell.

as I don't have much knowledge regarding to Cancer

for first part i cant say anything but for second part regarding to favor or disfavor i will go for favor because although they have some side effects but still they are at least saving lives and i think its better to see a person rather than never seeing them.

regarding to target some persons are less prone to cancer due to their genetic build up, their routine, their habits.

i think yes chemo therapies are becoming more successful with more knowledge .. i am not in much touch with that but i think by gaining knowledge we would be surely able to go fro targeted drug delivery systems

One of the newest criticisms raised about chemotherapy is cancer stem cells. When we perform chemotherapy we could kill cancer cell but not cancer stem cells. Because cancer stem cells are more renitent against most of chemotherapy. In lake of "differentiated cancer cells" cancer stem cells become more aggressive and renewal more. Therefor cancer relapses and becomes more invasive. More cancer stem cells = More resistance against therapy and relapse

In general, cancers or leukemia with high mitotic rates are the more susceptible to conventional chemotherapy, but there are some exceptions. Some cancers are difficult to treat by chemotherapy because they are in a location where high drug concentration is difficult to achieve.

The major principle in conventional chemotherapy is that it targets highly dividing cells. However, normal hematopoietic cells divide much more than the large majority of cancers, so there should be some specific mechanism that permits to use them, and my impression is that specificity is very often determined empirically. Still myelosuppression remains the main limitation of chemotherapy.

http://www.youtube.com/watch?v=FBLnL4XA6fc

http://onlinelibrary.wiley.com/store/10.1002/cam4.91/asset/cam491.pdf;jsessionid=7C8A742C8A78A7EA04809A7FCEB62CCC.f02t04?v=1&t=hpvh4v8v&s=b6458cd1a6e5dfab92ce72914d59a2f83b42887e

New, targeted, chemotherapies can be specific to a signalling pathway, but a very significant clinical benefit has only be obtained, to my knowledge, in Chronic Myeloid Leukemia, which might be viewed as a pre-malignant condition rather than a full blown malignancy.

Some therapeutic antibodies, like anti-CD20, target a specific cell type, leading to the elimination of B cells expressing CD20, which can be tolerated by the organism.

Finally, antibodies which increase immune response have been shown to bring significant clinical benefit. However, it is not clear why they are efficient in some patients and not others.

@ Babak

The principle of chemotherapy series is, in part, to put the cells that were resting in cycle, so that they would be killed at the next step. And if the cells remain resting rather dividing, there is no more cancer problem (or the same as in cancer with low mitotic rates).

chemotherapies work by kill mitotically active cells. Chemotherapies work the best when cancerous cells are primed; more adept to undergo apoptosis. Tumors are known to be heterogeneous in microenvironment organization, differentiation plasticity, priming, ect.

Limitations of chemo involve avoiding toxicity of healthy tissue and minimizing side effects. Blood producing cells of the bone marrow are highly diving and are targets for chemotherapies. Interference with hematopoiesis in the bone marrow converges to fatigue( Low RBC), bleeding(Low Platelets), infection(Low WBC) as stereotypical risk factors for many treatments.

The success rate for most cancers is roughly 50% for the first 5 years.

Cancers with the worst success rates are: pancreatic, Liver, Lung. Due mainly to the proganosis of the cancer being difficult to detect; cancers are highly developed by time detection occurs.

As mentioned previously, key to effective treatment involves depletion of minority resident CSCs to prevent relapse via repopulating the tumor

(a) 90% of cancer patients die from their metastases that are frequently resistant to apoptosis. (b) Different types of primary cancers (i.e. glioblastomas, melanomas, pancreas cancers, NSCLCs) are also apoptosis-­‐‑resistant. More than 80% of current chemotherapeutics are pro-­‐‑ apoptotic agents, and targeted therapies (i.e. Mabs, kinase inhibitors) display weak to no efficiency against these cancers. Hence, new types of cytotoxic/cytostatic compounds are mandatory to combat apoptosis-­‐‑resistant cancer cells and/or multidrug resistant ones.

Targeting cancer is not simple as it possess the similar targets as the normal cells have. Therefore selectivity is the major issue whereas the other issues like toxicity and resistance must need to be addressed. But recent up-gradation in cancer biology bring better perspectives especially in case of understanding the behavior of a cancer cell.

In principle it is accepted that cancer cells with high mititic rate are respond to chemotherapy. Of course there are multiple parameters to determin whether a patient will have a benefit from chemotherapy . Basically the criteria are:

1. The mitotic rate of the cells (most of chemothery agents are cell cylce depended with exception of alkyliating agents etc)

2. The prior therapy of the patient

3. Specific markers which indicated whether this patient is able to activate most of the chemotheray agents effectively to their active form (like DPD, MGMT UTGA1 etc)

4. Location of the tumor (despite that in cell cancer culture we may notice effect, in an organism level the agent may never reach the area where the tumor locates)

5. Performance status of the patient (normaly patients are classified according to ECOG scale or Karnofski index and we assess whether the side effects of chemotheraoy is less than the benefit).

So the all process of assessment is not so easy and this is the reason why we introduce the idea of MDTs (despite the fact that rarely is applicable in clinical practise).

You are right, Ioannis, but I should add that alkylating agents preferentially act on highly dividing cells too, because quiescent cells have enough time to repair their DNA before entering cell cycle.