**4. Consideration of adverse events**

When considering second-line therapy, clinicians must be aware that, by definition, patients receiving second-line therapy are not chemonaive and experience treatment failure; thus, they are more likely to be resistant to therapy than first-line treatment. Furthermore, patient performance status is more likely to deteriorate due to a recurrent cancer burden and treatment against it. Indeed, widely ranging grades of gastrointestinal symptoms-related adverse events occurred in a substantial proportion of patients in the BSC arms of clinical trials, suggesting a poor quality of life even by the BSC. In addition, a more intensive regimen aiming at a prolonged OS may cause a higher likelihood of severe adverse events that may result in treatment discontinuation and limitation. For example, the DCF regimen caused 82% of grade 3-4 neutropenia and 29% of febrile neutropenia. Therefore, balancing efficacy and adverse events should be taken into account when developing second-line therapy. The development of more intensive while less toxic second-line regimens could be positioned as a breakthrough marker of GC treatment, which can then ultimately achieve further survival prolongation without treatment withdrawal.

In this context, another direction for research is to establish less toxic regimens with preserved anticancer activity. As described earlier, the conventional first-line treatment comprises 5 fluorouracil and emetogenic/nephrotoxic cisplatin. Therefore, the challenges for a less toxic regimen are the substitution of oxaliplatin for nephrotoxic cisplatin [27,28] or substitution of oral capecitabine for intravenous 5-fluorouracil [29]. Such substitutions aim to reduce toxicity and maintain organ function, thus avoiding treatment withdrawal and prolonged treatment duration.

Fluorouracil, leucovorin, and oxaliplatin (FLO) were associated with significantly less anemia, nausea, vomiting, fatigue, renal toxicity, and serious adverse events related to the treatment as compared with fluorouracil, leucovorin, and cisplatin (FLP) [27]. In addition, there was a better trend toward improved median PFS by FLO than FLP. Similarly, as compared to SP, S-1 plus oxaliplatin (SOX) resulted in a reduced risk of grade 3/4 neutropenia (41.5% vs 19.5%) and febrile neutropenia (6.9% vs 0.9%) while median PFS was similar between the two regimens (5.4 months versus 5.5 months) [28]. These findings further support the possibility that the substitution of oxaliplatin for cisplatin reduced toxicity while maintaining efficacy. Accordingly, length of hospital stay per cycle of SOX regimen (0.85 day) was significantly shorter than that for the SP regimen (6 days) [28]. Furthermore, capecitabine and cisplatin (XP) versus 5-fluorouracil and cisplatin (FP) proved similar median OS (10.5 months versus 9.3 months), suggesting that the inconvenience of infusional 5-fluorouracil could be replaced by oral capecitabine, thus realizing a more simplified dosing schedule [29]. Whether this concept can be applied to second-line therapy warrants further investigation.

## **5. Future perspectives**

patients with ERBB1 overexpressed advanced GC [26]. This is a Japan and Korea collaborative

**Figure 2.** Comparisons of median OS between the previous RCTs. The percentage indicates the proportion of patients receiving further therapy in each trial. The reference numbers are expressed in brackets. \*; first-line trials, BSC; best supportive care, PBO; placebo, Cape; capecitabine, Ox; oxaliplatin, EOC; epirubicin, oxaliplatin, and capecitabine, ND;

12.2

0 2 4 6 8 10 12 14

10.5

Median overall survival time (months)

11.3

11.4 11.5

11

8.8

8.6

5.9

9.4 10.7

9.6

8.9 8.4 9.5 10.7 10.1

7.4

The results of some trials have been published; however, at present, trials in which the primary endpoint has been met have been unfortunately very limited. The positive results hitherto obtained include a prolonged PFS by a combination of irinotecan and cisplatin after the failure of S-1 based first-line chemotherapy, and prolonged PFS and OS by ramucirumab in combi‐ nation with weekly paclitaxel. The results of other studies, especially using molecular targeting

When considering second-line therapy, clinicians must be aware that, by definition, patients receiving second-line therapy are not chemonaive and experience treatment failure; thus, they are more likely to be resistant to therapy than first-line treatment. Furthermore, patient performance status is more likely to deteriorate due to a recurrent cancer burden and treatment

RCT allocating patients at 1:1 ratio for a total of approximately 400 patients per arm.

agents, are awaited.

ND ND ND ND 53% 53% 38% 36% 75% 75% ND ND ND ND 72% 90% 75% 75%

LoGiC\* [41]

not described.

[40]

[39]

Western

Japanese

[24] TYTAN [22]

REAL‐3\*

EXPAND\*

[23],

[23],

RAINBOW

WCOG4007

GI‐0801

[19]

[17]

Figure 2

108 Updates on Cancer Treatment

RAINBOW

RAINBOW

**4. Consideration of adverse events**

Lapatinib+Cape/Ox PBO+Cape/Ox Panitumumab+EOC

Cetuximab+Cape/Ox Cape/Ox

Ramucirumab+weekly Paclitaxel PBO+weekly Paclitaxel Ramucirumab+weekly Paclitaxel PBO+weekly Paclitaxel Ramucirumab+weekly Paclitaxel PBO+weekly Paclitaxel Lapatinib+weekly Paclitaxel weekly Paclitaxel Irinotecan Paclitaxel

biweekly Irinotecan+Cisplatin biweekly Irinotecan

EOC

With the development of a new generation of cytotoxic agents and molecular targeting agents, the research field of GC treatment appears to be transitioning into a new era with a focus on the targetable molecules in GC. Several molecular targeting agents are currently being evaluated both in first- and second-line settings. The pending results of ongoing clinical trials motivates researchers to continue the challenge of establishing the best second-line regimens or less toxic combinations for the treatment of advanced GC.

**a.** Clarifying the genetic alterations of targeted molecules and their interactions.

Unfortunately, in sharp contrast to colorectal cancer in which there has been a significant achievement in treatment by the use of molecular targeting agents, only one agent (ramucir‐ umab) has been currently proved to be an agent for second-line therapy presumably due to the genetic complexity and molecular heterogeneity of the disease.

Recent findings have highlighted the mechanisms of the actions of molecular targeting agents or patterns of expression of targetable molecules in several tumors. For example, genetic alterations that are critical for cell growth occur with considerably different frequencies, being 60%, 33%, and 32% in cancers of the pancreas, biliary tract, and colon, respectively [30]. Furthermore, certain combinations of targets are expressed in a mutually exclusive or cooccurring manner in the same tumor. A mutually exclusive fashion would be a case being KRAS and BRAF in colorectal cancer, or ERBB1 and KRAS in lung cancer [31]. The co-occurring expression of targets is a case of being ERBB2 and PIK3CA in breast cancer [32]. With regard to GC, although KRAS mutations are initially recognized as an infrequent phenomenon in GC [33], the alterations and amplifications of other genes --both known or previously unreported- have been subsequently found in a substantial number of GC patients in a mutually exclusive manner [34,35] or co-amplified manner [36]. These findings create a challenge in the treatment regimen with either a use of each blockade of each targetable molecule or a use of dual- or paninhibitors of kinases [37]. In addition, elucidation of the roles of each domain in ERBB2 that plays a role in resistance to anti-HER2 therapy further provides the theoretical basis to modify therapeutic strategies to circumvent this resistance [38]. These advances may expand thera‐ peutic options, thereby making larger proportions of GC patients possible candidates for molecular targeting therapies than previously appreciated. Accordingly, there may be a desperate need for multiple gene profiling which could help establish rational molecular criteria for patient inclusion and exclusion in clinical trials. Patient selection by gene profiling may allow better patient recruitment for those most likely to respond to targeted therapies.

**b.** Positive and negative interactions between chemotherapy and molecular targeting therapies.

It should be noted that the recent clinical trials of first-line molecular targeting therapies regrettably resulted in some negative results [39-41] (Figure 2). The addition of cetuximab to cisplatin plus capecitabine had a similar median PFS (4.4 months) and median OS (9.4 months) compared to cisplatin plus capecitabine alone (5.6 months and 10.7 months, respectively) [39] (EXPAND). Surprisingly, the addition of panitumumab to epirubicin, oxaliplatin, and capecitabine (EOC) resulted in a significantly shorter (p=0.013) median OS (8.8 months) compared to EOC (11.3 months) (REAL-3) [40]. Furthermore, lapatinib in combination with capecitabine and oxaliplatin could not show any significant survival benefit (LoGiC) [41]. These negative results lead to speculation that there may be ideal combinations or compati‐ bility between chemotherapy and molecular targeting therapy. In addition, even the addition of panitumumab to EOC achieved only similar median OS to those of the WCOG 4007 trial (Figure 2) [19,40]. Therefore, a certain combination, such as anti-EGFR antibody and capeci‐ tabine or oxaliplatin, may be ineffective or even interfere with the other. This speculation can be supported by the observation that addition of cetuximab to oxaliplatin plus fluoropyrimi‐ dine-based chemotherapy failed to demonstrate survival benefits for advanced colorectal cancer [42].

**c.** Need to evaluate the updated molecular profile.

Another obstacle for the progression of second-line treatment lies in the possibility that the molecular profile of GC is likely to change under the stress of treatment. Generally, lower response rates and shorter survival times in patients receiving second-line therapy than chemonaive patients may partly be explained by such molecular changes that lead to a resistance to therapy. Ideally, the on-demand tissue samples from tumor sites currently of interest are needed to assess the updated genetic and molecular patterns and to predict whether the planned second-line therapy is really effective. However, direct tumor tissue sampling and subsequent gene analysis are often hampered by virtually inaccesible tumor localization and by overly small sample volumes to perform gene analysis. It is necessary to discover novel markers which can be alternatives for those obtained only by direct tumor tissue sampling as well as to improvise new methods to assess them in order to select the right patients for the right second-line regimen.

Motivated by the first promising results of trastuzumab use in the ToGA trial, several molec‐ ular targeting therapies have been challenged in clinical trials. Continuous efforts should be necessary to clarify the mutation and amplification of targeted molecules, and novel methods for their genetic profiling should probably become part of clinical routines. Ultimately, GC patients harboring unique genetic profiles of targeted molecules should be allocated into specific, suitable trials. Targeted therapies tailored to individual genetic profiles maximize treatment efficacy because this allows the recruitment of selected, most suitable patients rather than unselected ones [43].

## **6. Conclusions**

**a.** Clarifying the genetic alterations of targeted molecules and their interactions.

the genetic complexity and molecular heterogeneity of the disease.

Unfortunately, in sharp contrast to colorectal cancer in which there has been a significant achievement in treatment by the use of molecular targeting agents, only one agent (ramucir‐ umab) has been currently proved to be an agent for second-line therapy presumably due to

Recent findings have highlighted the mechanisms of the actions of molecular targeting agents or patterns of expression of targetable molecules in several tumors. For example, genetic alterations that are critical for cell growth occur with considerably different frequencies, being 60%, 33%, and 32% in cancers of the pancreas, biliary tract, and colon, respectively [30]. Furthermore, certain combinations of targets are expressed in a mutually exclusive or cooccurring manner in the same tumor. A mutually exclusive fashion would be a case being KRAS and BRAF in colorectal cancer, or ERBB1 and KRAS in lung cancer [31]. The co-occurring expression of targets is a case of being ERBB2 and PIK3CA in breast cancer [32]. With regard to GC, although KRAS mutations are initially recognized as an infrequent phenomenon in GC [33], the alterations and amplifications of other genes --both known or previously unreported- have been subsequently found in a substantial number of GC patients in a mutually exclusive manner [34,35] or co-amplified manner [36]. These findings create a challenge in the treatment regimen with either a use of each blockade of each targetable molecule or a use of dual- or paninhibitors of kinases [37]. In addition, elucidation of the roles of each domain in ERBB2 that plays a role in resistance to anti-HER2 therapy further provides the theoretical basis to modify therapeutic strategies to circumvent this resistance [38]. These advances may expand thera‐ peutic options, thereby making larger proportions of GC patients possible candidates for molecular targeting therapies than previously appreciated. Accordingly, there may be a desperate need for multiple gene profiling which could help establish rational molecular criteria for patient inclusion and exclusion in clinical trials. Patient selection by gene profiling may allow better patient recruitment for those most likely to respond to targeted therapies.

**b.** Positive and negative interactions between chemotherapy and molecular targeting

It should be noted that the recent clinical trials of first-line molecular targeting therapies regrettably resulted in some negative results [39-41] (Figure 2). The addition of cetuximab to cisplatin plus capecitabine had a similar median PFS (4.4 months) and median OS (9.4 months) compared to cisplatin plus capecitabine alone (5.6 months and 10.7 months, respectively) [39] (EXPAND). Surprisingly, the addition of panitumumab to epirubicin, oxaliplatin, and capecitabine (EOC) resulted in a significantly shorter (p=0.013) median OS (8.8 months) compared to EOC (11.3 months) (REAL-3) [40]. Furthermore, lapatinib in combination with capecitabine and oxaliplatin could not show any significant survival benefit (LoGiC) [41]. These negative results lead to speculation that there may be ideal combinations or compati‐ bility between chemotherapy and molecular targeting therapy. In addition, even the addition of panitumumab to EOC achieved only similar median OS to those of the WCOG 4007 trial (Figure 2) [19,40]. Therefore, a certain combination, such as anti-EGFR antibody and capeci‐

therapies.

110 Updates on Cancer Treatment

Against the background of survival advantages of second-line therapy over BSC in GC patients refractory to first-line treatment, efforts to establish the most effective regimens have been just begun. Parallel to the development of molecular targeting agents, the investigated regimens comprise doublet or triplet chemotherapeutic agents, molecular targeting agents, and their combinations. In addition, the minimization of adverse events should be taken into account to avoid treatment discontinuation. There is a desperate need to explore genetic mutations of targeted molecules and the interactions between them, to establish novel methods to assess them, to clarify the positive or negative interactions between chemotherapy and molecular targeting agents, and to find regimens in which adverse events are least likely to occur for avoiding treatment discontinuation. These could help determine rational molecular criteria for patient inclusion and exclusion in clinical trials, realize the most efficient patient recruit‐ ment for those most likely to respond to therapies, and accelerate the establishment of the most effective second-line therapy that could achieve greater survival prolongation.
