## 1 Introduction  
Danshen or Tanshen, the dried root or rhizomes of _Salvia milliorrhiza_ Bunge, has been used in Traditional Chinese Medicine (TCM) in China and many Asian countries as preventive or therapeutic remedies for coronary heart diseases, vascular diseases, stroke, hyperlipidemia, endangitits, arthritis and hepatitis [1,2]. Fufang Danshen, a composite multi-herbal TCM formula containing Danshen as the major ingredient, is officially listed in the _Chinese Pharmacopoeia_ for many indications. Fufang Danshen Dripping Pill (one of the commercial forms of Fufang Danshen) has completed Phase II clinical trials for evaluating the efficacy and safety in patients with chronic stable angina pectoris in the USA (No. NCT00797953).  
Since the 1930s when tanshinones were first isolated from Danshen by [PERSON] _et al._[3], more than 90 chemical constituents have been identified. They can be classified into two major groups: more than 40 lipophilic constituents [2,4] and more than 50 hydrophilic compounds, respectively [1]. Tanshinones are a class of lipophilic abietane diterpene compounds, including cryptotanshinone (CT), tanshinone IIA (TIIA), tanshinone I (TI), dihydrotranshinone I (DH-TI) (Figure 1), isotanshinone I, tanshinone IIB, methyltanshinone, isocryptotanshinone I, isocryptotanshinone II, _etc._[1,4-9]. More recently identified structurally-related tanshinlactone and neo-tanshinlactone (Figure 1) have been reported to be more potent for anti-cancer activities [2]. Hydrophilic constituents from Danshen include danshensu (also known as salvianic acid A or salvianic acid B), protocatechuic acid, protocatechuic aldehyde, rosmarinic acid, salvianolic acid A, salvianolic acid B, and salvianolic acid C (the last three also known as lithospheric acids A-C, or magnesium tishopermates A-C, ortanshinonates A-C), _etc_. [1,5,10,11]. In addition to these two major classes of constituents, baicalin, 5,3'-dihydroxy-7,4'-dimethoxy flavoure, unsolic acid, \(\beta\)-sitosterol, daucosterol, vitamin E and tannin have been identified from Danshen [12]. Numerous studies reported the isolation, identification, synthesis, bioactivities, pharmacokinetics and pharmacology of Danshen constituents. Tanshinones and hydrophilic constituents from Danshen have been extensively investigated for the cardiovascular activities [13, 14, 15, 16].  
The chemistry and biosynthesis as well as total chemical synthesis of tanshinones have been thoroughly reviewed by [PERSON] and colleagues from the Natural Products Research Laboratories, University of North Carolina, Chapel Hill, North Carolina [2,4]. The anti-cancer properties of tanshinones or tanshinone-containing herbal formula have been investigated more recently. TIIA and CT are the two most extensively studied in this respect, followed by TI and DH-TI. These tanshinones exhibit broad anti-cancer properties in cell culture models, which had been discussed to some extent in several reviews [2,4,17], but pharmacokinetics of tanshinones have not been systematically reviewed.  
In this article, we review the natural and alternative sources of tanshinones and their pharmacokinetic characteristics. We provide an in-depth analysis of anti-cancer activities _in vitro_ and in preclinical animal cancer models. We update information on cancer-related clinical studies of TIIA and tanshinone-containing TCM formulas. The databases PubMed, SciFinder and CAJViewer (full text articles in Chinese) were used to search literatures covering 1930s-July 2012.