Basically the reason that Cisplatin is used first instead of carboplatin is that most of the studies done used cisplatin so it has a track record
. Plus several studies cite a 1998 meta analysis that indicated cisplatin was better than carboplatin for head and neck tumors. Carbo vs Cis study

Cisplatin is called the �penicillin of cancer� because it is used so widely and it was the first big chemotherapy drug. Cisplatin also plays an interesting role in the history of chemistry. First synthesized in the 1800s, long before anyone thought of using it against cancer Cisplatin and carboplatin as cancer agents were discovered by accident in the 1960s when Michigan State University researchers used platinum electrodes for some experiments. The researchers though that the electrodes would be �inert,� i.e. that they would not react chemically. But when an electric current was applied, it reacted with the growth medium to form filaments that interfered with cell division. The researchers reasoned that this might be useful in cancer treatment, and the drugs were eventually patented in the 1970s.

Carboplatin's patent expired in 2002. Cisplatin's expired back in the 1996 but Bristol tried a second patent in 1995 that was overturned by a district court and then appeals court in 2002. Accordingly, there is no financial incentive for any drug company to spend the money necessary for clinical trials comparing cisplatin and carboplatin for oral cancer. Any drug manufacturer can make either one without paying royalties.
Contrast that to Erbitux which is patented hence all the clinical trials and studies being pushed and financed by the patent owner. Even the big RTOG study whose results will finally settle the Erbitux issues here, pits Erbitux against cisplatin, not carboplatin.

In two trials comparing cisplatin and carboplatin for ovarian cancer in the carboplatin package insert on Bristol Myers Squibb web site, cisplatin had a small edge in 3 year progression free survival, 23% to 19% in the NCIC trial and 14% to 8% in the SWOG trial but overall survival rates (allowing recurrences) were better for carbo in the Canadian study but worse in the Southwest study.

So at this this point, oncologists juggle the toxicity of cisplatin and the slight differences in the studies. I do not see any scenario of funding going to resolve which of two old patent expired drugs is better. Too bad for oral cancer patients though. The one bright spot is a June article in the Indian Times about a potential breakthru to have cisplatin efficacy with carboplatinum's less toxicity:
[quote]
They increased the size of Cisplatin by joining it with cholesterol. The enlarged molecules are too big to get into the body tissues and damage them but cancer cells have larger pores that let them through. In lab studies, the conjugate drug was shown to be far less toxic, but highly effective.
Sengupta and Mashelkar have set up a Delhi-based company, Invictus Oncology, to take this modified Cisplatin to the market. Invictus had licensed the technology from the non-profit Partners Healthcare, founded by the Brigham And Women's Hospital in Harvard, where the research was carried out.
Charm[/quote]